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241 Cards in this Set
- Front
- Back
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What is geographic information?
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A set of tools and procedures used to
collect, manage, analyze, and display spatially-referenced (ie. mapped) information |
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Why does GIS Matter
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Almost everything happens somewhere
Knowing where some things happen is critically important Position of country boundaries Location of hospitals Routing delivery vehicles Management of forest stands Allocation of funds for sea defenses |
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1) Define: Geographic
2) Define: Spatial 3) Define: Geospatial |
1)Earth’s surface and nearsurface
2)any space (including geographic) e.g. medical imaging 3)synonymous with geographic |
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Define: Scale
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Level of geographic detail
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Define: Intent (two focuses)
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Normative – focus on design
Positive – focus on advancing science |
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Why is GIS Special
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Multidimensional
Voluminous Can be represented at different levels of spatial resolution May be represented in different ways inside a computer Requires projection to flat surface Unique analysis methods Analysis is time-consuming Data updates are complex and expensive Map displays require fast data retrieval |
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Q= decision making support infrastructure
A= Ease of sharing Q: Wisdom Knowledge Evidence Information Data |
A:
Impossible Difficult Often Not Easy Easy Easy |
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Information on the World
1) How it looks = ? 2) How it works = ? 3) Knowledge about process is more valuble than form because it can be used to ______ |
1)form
2)Process 3)predict |
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GIS Combine what two things?
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General scientific knowledge in software
Specific information in databases |
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Problem Solving:
Objective or goal is what? |
often maximize or
minimize (cost, distance) |
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Problem Solving:
difference between Tangible and intagible |
Tangible (well defined scale) vs intangible -
e.g. quality of life, environmental impact |
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Problem Solving:
example of Multiple objectives |
e.g. cost and
environmental impact Multi-criteria decision-making techniques |
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GISystem - Defined
1) Container of _______ 2) Computerized tools for _____ ______ _______ 3) ________ decision support system 4) ________ _______ of geographically distributed features and facilities 5) ool for revealing _______ and _______ in geographic information 6) Tool to automate ________ _________ _______ |
1) maps
2) solving geographic problems 3) Spatial 4) Mechanized inventory 5) patterns and processes 6) time-consuming tasks |
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Brief History of GIS
1960 – 70s Innovation |
First GIS – Canada Land Inventory
DIME US Bureau of Census Harvard Laboratory for Computer Graphics Major vendors started (e.g. ESRI, Intergraph) Landsat satellite launched Key academic conferences (e.g. AutoCarto) |
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Brief History of GIS
1980s Commercialization |
Commercial GIS software (e.g. ArcInfo)
First GIS textbooks First global data sets Clinton Executive Order |
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Brief History of GIS
2000s Exploitation |
Internet becomes major deliver vehicle
More than 1 million active users |
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Geographic Information System is an Organized collection of
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Hardware
Software Network Data People Procedures |
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Business of GIS
Worth? applications of use? |
GIS industry is worth over $7 billion
(very likely over $10,000,000,000) Software Data Services Publishing Education |
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Define GISystems
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Emphasis on technology and tools
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Define GIScience
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Fundamental issues raised by the use of GIS and
related technologies, e.g.: • Spatial analysis • Map projections • Accuracy • Scientific visualization |
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Define GIStudies
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Systematic study of the use of geographic
information |
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Social Implications of GIS
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Favors generalization, possibly at expense of
minorities and individuals Use is not always neutral and can be applied to military and industrial surveillance Tendency to be technological rather than human need focused Maintains and extends the status quo of societal power structures Absence of GIS in critical research |
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5 Ms of Applied GIS
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Mapping
Measuring Monitoring Modeling Managing |
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Roger's Diffusion Model
Innovators Early Adopters Early Majority Late Majority Laggards |
- risk takers
- opinion formers - peers followers - mass market trend followers - oriented to the past |
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Many environmental applications of GIS
- Natural ______ inventory - Environmental ________ - Sustainable _________ -,Precision _______ - Natural ______ mitigation - Environmental _______ analysis |
-resouce
-remediation -development -agriculture -hazard -impact |
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Planning scales
Operational Tactical Strategic |
- processing day-to-day transactions
(e.g. delivery vehicle routing) - allocation of resources to short-term (weekly) problems (e.g. target marketing promotional campaigns) - longer term goals and missions (e.g. store location planning) |
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how much of what we see is a representation
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everything: a story, a picture, a map, even what you see is just light and you may not see something that is behind something else. it is only a representation
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Types of Attributes (give example)
Nominal Ordinal Interval Ratio Cyclic |
- land cover class
- ranking - Celsius temperature (Differences make sense) - Kelvin temperature (Ratios make sense) - wind direction |
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Cyclic Attributes
Do not behave as other attributes - What is the average of two compass bearings, e.g. 350 and 10? - when do they occur in GIS? |
- 360
- Wind Direction, Slope aspect, flow direction |
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What are discrete objects?
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- The world as a table-top
- Objects with well-defined boundaries - Points, lines, and areas Countable Persistent through time, perhaps mobile Biological organisms Animals, trees Human-made objects Vehicles, houses, fire hydrants |
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what is a field?
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- Properties that vary continuously over space
- Elevation as the archetype --A single value at every point on the Earth’s surface - The source of metaphor and language - Any field can have slope, gradient, peaks, pits |
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What is value in a field?
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- Value is a function of location
Property can be of any attribute type, including direction |
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what are some examples of fields?
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- Soil properties, e.g. pH, soil moisture
- Population density But at fine enough scale the concept breaks down Identity of land owner - A single value of a nominal property at any point - Name of county or state or nation - Atmospheric temperature, pressure |
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what are characteristics of raster data?
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- Pixel size
The size of the cell or picture element, defining the level of spatial detail - All variation within pixels is lost - Assignment scheme |
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what is an assignment scheme ?
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The value of a cell may be an average over the
cell, or a total within the cell, or the commonest value in the cell It may also be the value found at the cell’s central point |
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What is vector data in the form of?
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- Points lines and areas respresented using coordinates
- areas are polygons |
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Raster vs Vector
- Volume of data |
Raster becomes more voluminous as cell size
decreases |
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Raster vs Vector
- Source and use of data |
- Remote sensing, elevation data come in raster form
- Vector favored for administrative data |
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Raster vs Vector
- Software |
Some GIS better suited to raster, some to vector
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What is spatial heterogeneity
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Differences in one spot in space vs another.
No two places in space are the same. |
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Why does GIS matter?
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- Small things can be intricate which makes a blown up map useful
- You can get lost in large areas so a shrunk map can be useful |
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What does GIS accomodate?
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Error and Spatial heterogeneity
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What is the first law of geography?
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- Everything is related to everything else
but near things are more related than distant things |
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Who wrote the first law of geography?
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Waldo Tobler in 1970
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What is spatial autocorrelation?
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- degree to which near and more distant things are interrelated
- Spatial autocorrelation is determined both by similarities in position, and by similarities in attributes |
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What is interpolation?
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calculating the value between two sampled points using the first law of geography.
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how can you relate autocorrelation to temperature, time and elevation?
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- temperature and elevation should be a similar value to the value sampled is near by
- an object moving in a direction will be near its start location if a short amount of time has passed |
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What is the range of Meranz Correlation?
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-1.000 to +1.000
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what is a -1.000 Meranz Correlation? +1.000?
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- (-1.000) = 100% negatively correlated (checkered board)
- (+1.000) = 1000% positively correlated (all the same type) |
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what is random Meranz Correlation?
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0.000
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what is a high Meranz Correlation value and what does it look like?
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.850 half one type and half the other. bigger the area with separated by the two types the higher the autocorrelation but never will be +1.000
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what determines how good geographic data is?
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only as good as the samling scheme used to create them.
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all geographic representations are ________
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samples
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when making a sample when does the probability of selection need to be?
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random and equal across all frames before starting to sample
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what is a sample frame?
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the study area
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Types of samples:
Random |
random points taken throughout the frame. can be disproportionate to the actual population, especially if the sample size is small
-random |
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Types of samples:
stratified sampling |
used in periodicity. over slow changes on large sxpanses of area to ensure even coverage. not advised for fast changing uneven areas (like using intersections to determine the commercial density of a city)
-checker board |
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Types of samples:
stratified random sampling |
to ensure an area is completely covered. it divides that frame into many smaller frames and takes a random sample inside the small frame.
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Types of samples:
stratified sampling with random variations in grid spacing |
keeps total frame sampled while giving more of an area a chance to be randomly selected
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Types of samples:
clustered random sampling |
used for frames in which the subject matter is only present around each other. (plants that grow around each other, sampling a mall for demographics)
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What is map generalization?
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- When data in a map is lost by simplifying its features
- Created either by accident or on purpose to save space |
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how is giving Iowa a slope value of 0 a generalization?
What is good? What is bad? |
- Iowa is not completely flat (ergo not 0), its has a slope that might be very steep in certain places
- This could be good for mapping the general topography of the United states - Bad at small scales because it lies |
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Why is it important to know how much data loss has occurred?
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You need to know how much you can trust the data.
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How can we guesstimate how much data has been lost?
What is this called? |
-We can measure the distance between the data and the real world.
This is called uncertainty |
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What is metadata?
Why is it important? |
- metadata is information that literally explains each color, feature and data set on a GIS. (data about data)
This is important so that you can tract someones steps to achieving an answer. It is a way to dramatically reduce uncertainty. |
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What would be impossible without metadata?
Does metadata only relate to GIS? |
- Find data in a library, search the WWW validate a maps accuracy.
- no it relates to anything that has data and most things have data |
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is a map in a map created at a RF=1:1200 more accurate than a map at RF=1:100,000?
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- no not necessarily. at each scale levels maps have certain tolerances that they are given and if they are inside those tolerances then they are considered accurate
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Why is a map at a small scale that is off by 2000 feet not necessarily more inaccurate than a large scale map thats off by 40 feet?
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- Maps are made at a certain scale for a reason and if they cannot be asked to be more accuate then the scale they were meant to be mapped at.
- if you need to scale down more accurately then you need a new map with a larger scale |
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What is Database Generalization?
Is it permanent? |
- when data is rounded or inflated to achieve a desired cartographic outcome
- this kind of generalization is permanent |
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What is cartographic generalization?
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- When the features on a map dont match the data they are representing in order to reach a cartographic outcome.
- this form of generalization is not permanent |
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Methods of Generization:
Simplification |
- wedding out points
- throwing out data that may have too many points |
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Methods of Generization:
Smoothing |
- eliminating or sometimes adding points to existing data to achive a smoother line or polygon
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Methods of Generization:
Collapse |
- replacing an area with a point or line
- sometimes happens on its own it the borders of polygons are too think - sometimes desired for simplification |
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Methods of Generization:
Aggregation |
- taking a large number of symbols representing, say trees, and replacing them with less symbols of trees
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Methods of Generization:
amalgamation |
- taking a large number of areas representing, say a person's property, and replacing them with less houses to signify a neighborhood
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Methods of Generization:
Merging |
- replacing several line objects, say a few roads with one or few roads
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Methods of Generization:
Refinement |
- replace complex patterns/objects, say a watershed, with a simpler representation with less streams
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Methods of Generization:
Exaggeration |
- relative enlargemnt of objects.
- attempts to counter an unwanted feature of collapse |
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Methods of Generization:
Enhancement |
- when a symbol, say a church on a 1:100,000 scale map, is larger than the object it is representing
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Methods of Generization:
Displacement |
- moving objects, say a railroad and a road, apart so that they can be seen where in real life they are right next to eachother
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what does The Douglas-Poiker algorithm do?
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- it drops the number of points in a line using a user-defined tolerance distance.
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How is merging regulated/decided on a map?
what is the minimum threshold called? |
-by tolerances set by the user at different scale levels
- if the feature falls below the threshold it is merged - Minimum Mapping Unit or MMU |
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How can a digital database have scales?
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- the user sets scale levels that act as flip points between a larger scale map and a smaller scale map
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What is Spatial Resolution?
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- the smallest distance over which change is recorded
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why is spatial resolution easy for vector data but more difficult for raster data?
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- Vector data is a series of points which do not have size theoretically so it can classify very small changes in an area.
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Why is spatial resolution difficult for raster data?
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- changes in features or zones at in a small area may not be depicted because raster data the feature with the largest contents in the pixel
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why does GIS matter?
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- sometimes its easier to see relationships between features when they are seen in space
- sometimes questions concerning proximity of one feature to another is most accurately and most easily answered via GIS - almost everything happens somewhere |
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Why is geographic data special?
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- it relates to almost everything
- multidimensional (height, width, length) - unique data analysis methods - can be represented different ways inside a computer (raster, vector) |
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In the context of information what is the difference between form and process?
What is more important? |
- form is how it looks (database)
- Process is how it works (software) - process is more important because it can be used to predict. - GIS combines scientific knowledge in software with specific information in databases |
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What is intent in terms of Geography? what are the two forms and how do they differ?
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- Intent is the purpose of a map
- the two types are: --Normative: focus on design (structure of a city, campus etc..) - Positive: focuses on advancing science (physics of water through soil, ecological relationships etc..) |
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What are the components/steps of using GIS?
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- Objective or goal: saves money and time
- Tangible Vs intangible: (tanglable) = well defined scale (intangible) = subjective to opinon, you know it when you see it but tough measure it (poverty) - Multiple objectives - (ex. weight cost vs. environmental impact) |
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what is the difference between GISystems. GIScience, and GIStudies?
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- GISystems attempts to solve problems using spatial data such as wildfire prevention
- GIScience is the scientific pursuit of different ways to map space, what on it, or attempt to understand the relationships between the different thing on it - GIStudies is the analysis of space and whats on it for intelligence purposes. |
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Why is interest in GIS building?
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- the need to know where boundaries are and understand the space around us become more important chiefly because we recently realized we dont know it
- also because it starting to get more crowded on this planet |
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Principles of map design:
Clarity |
- Examine your objectives
- Emphasize the main ideas - Remove anything that dilutes the message |
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Principles of map design:
Order |
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Principles of map design:
Balance |
- Every element has weight
- Weight must be equally distributed around the visual center - Maximize the map space, then manage other objects in relation to white space |
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Principles of map design:
Contrast |
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Principles of map design:
Unity |
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Principles of map design:
Harmony |
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Principles of map design:
What influences weight? |
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Concept of Visual Hierarchy:
Importance of figure-ground |
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Concept of Visual Hierarchy:
Hierarchical Organization |
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What are the rules of the subject area?
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- Most important
- Placed in the visual center - Make as large as possible - Place at top of visual hierarchy |
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Tittle Should be what? and not be what?
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- Placed where it has some importance and provides balance
- If more than one line, center - Main title should be heavier than subtitle - Short titles can be ALL CAPS - Should generally include theme, area, date - Should be both brief and complete - Never put “A Map of…” |
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Legend should what? and not be what?
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- Creates good balance
- Only set off in frame is necessary - Do not add word Legend or Key - Legend title should refine the map title - Any symbol that is not self-explanatory should be included in the legend - Symbols must look exactly the same |
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Scale should be what? and not be what?
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- All maps should include a scale but it should be placed well-down in the hierarchy
- Don’t make them too ornate - Don’t make them too accurate - Only include RF if final map scale is known |
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What is important about the orientation of a map?
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- Reader assumes north is at the top
- If north is not at top, direction indication is very important - North arrows are often misused |
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What is important about inset maps? Used for what?
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- Important not to overuse
- May be used to gain scale - Use to provide a wider context |
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What does the border do for the map?
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- Adds to map stability
- Keeps things from “floating in space” - Contains eye movement - Avoid multi-line borders - Neatline – often needed when one has primary map space vs. secondary - Can bleed the map |
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what is Supplemental Information in the context of cartography? whats in it?
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- Extremely important and often omitted
- Thematic data sources - Base data sources if exotic or required - Projection, datum, spheroid info |
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What are the 4 rules/things to watch out for in cartography when considering Typography Rules?
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- Main criteria = clarity
- All rules are VERY flexible - Name Placement - Size |
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What some basic guideline for choosing fonts on a map?
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- Use a single font
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When do you use serif font vs san serif font? how can you recognize it?
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- Serif is used for natural features
san serif is used for man made features - has a fat middle in the "S" and theres little notches at the ends of the S |
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What should you consider about you font when labeling water? What about states and regions?
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- Water features in italics, letters concisely-spaced, words should follow the feature
- All lines – bottom of letters should be closest to the line - Lakes and seas – completely in or out - States/regions – spread name out to over an area |
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What takes precedent over what, lines or letters? What dont you do to coastlines? What do you do if you have to break a feature boundary?
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- Letters
- Dont ever breaks coastlines - use a halo or a box |
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Georeferencing is essential because:
The method of georeferencing must be: |
- All information must be linked to the earths surface
- unique in that the place being referenced is only one place on earth - shared among many people so that that people know who, where or what the georeference is - persistent through time |
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Why must a georeference be unique in a defined domain but not the entire world?
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- there are many towns or cities in a country or the world that have the same name. Without a domain (state or a country and a a state) you would be georeferening all of them.
- there are many different springfields in the US, you need a state to narrow which one you are exactly talking about. |
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How can georeferences be measurements?
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- they define locations via measurements from fixed location (distance from the equator)
- could be based on ordering (on a given strip of road, they find out how many houses are on it, figure out the assignemnt sceme and assign a location to the place where they think it is bases on the house number) - names do not involve ordering or measuring |
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Placenames:
- what makes them so useful? - What makes them confusing? - what makes them chronologically constrained? |
- 1st and most used form of georeferencing
- one name can be referencing many different places - one name can reference cities, countries or continents - names can pass in and out of existance |
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Postal addresses and postcodes:
- How are streets unique? |
- Streets have names that are unique in local areas and local areas are unique in larger domains etc..
- if these assumptionas are true then postal addresses are useful georeferences |
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When do Postal addresses fail as georeferences?
- rural areas - natural features - when numbering on streets is not sequential |
- people that have long driveways that move laterally down a road, the georeference is where the driveway starts but the house is in a different location OR a few houses are spread out on a long road, but google says they are only a matter of meters apart
- lakes mountains etc cannot be georeferenced using zip codes - in japan houses do not number down a street so you need a different algorithm to figure out whats where |
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Postal zip codes as georeferences:
- how are they helpful? - how are they structured? |
- zip codes cover the whole US and are used in many countries. they also cover larger areas than postal zip codes
- 1st few characters define large areas and the rest define smller portions. |
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What is linear referencing?
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- Spatial referencing without a GPS.
- Achieved by listing a distance down a certain compas direction or along a road to define where a point is |
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What is liear referencing used for/by?
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- Used by transportation authorities to keep track of road condition and signs
- used by police for accidents or otherwise |
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How does linear referencing work?
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an intersection of two roads serve as a zero point and a bearing is usually measured in the same direction
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What are the drawbacks of linear referencing?
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- labor intensive, less accurate over long distances depending on measuring device (odometer)
- the same two roads may intersect more than once - intersection and end point of measurement may be far away from each other (rural areas) |
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What is a Cadaster?
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maps of land ownership showing property bounderies
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What is the Public Land Survey System?
How does it work? |
PLSS is a way of georeferencing a Cadaster.
Set an accurate North-South central meridian line and then measure six mile blocks in the east west direction from the central line. Each square is referenced by a town ownership number, the square can then be divided in to 160 acre squares. |
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Drawbacks of PLSS
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- the earth is not flat so the squares are not exactly 6 miles by six miles, but it is corrected for by resetting the size of the blocks on a regular interval
- Rough terrain works to make the six mile measurement less accurate as well |
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Latitude and Longitude as a Georeference:
Why use it? |
Most comprehensive and powerful method of georeferencing
- Uses a well defined and fixed reference frame (based on the earth rotation, center of mass and the greeenwich meridian) |
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What is needed to define Latitude?
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A model of the earths shape (a geoid)
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The earth's shape is somewhat ________. a defined _________ is used globally to model this shape and it is called the __________.
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- Elliptical
- Ellipsoid - WGS 1984 |
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The N-S diameter is roughly _/___ th smaller than the E-W diameter
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1/300th
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The WGS 1984 and the _______ are the same thing.
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NAD 1983
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An ellipsoid is the three dimensional shape obtained by rotating an ellipse about its _____ _____.
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- Minor axis
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Define: Geoid
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The true three dimentional shape of the earth considered as a mean sea level extended through the continents
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The geoid is measured in _ and _ meters difference from the ellipsoid.
- how is it calculated? |
+ and -
- It is calculated by measuring the gravitational force exerted by the earth in different places. - It is kind of like an average height of the topographic surface |
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What exactly is latitude a measurement of?
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The angle made from a point on the earths surface met with the plane of the equator. hence the reason latitude increases as you move away from the equator
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What is a datum?
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A set of parameters and points that help define the shape of the earths surface. It is part of the geographic coordinate system which helps define the planar coordinate system.
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an elipsoid is what the shape of the earth would be if ___________ .
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- it was perfectly flat and didnt have uneven dips and peaks throughout its surface
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What do projections attempt to do?
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- they attempt to display the curved earths surface on a flat piece of paper.
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Why use a projection?
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- The paper used to output GIS maps is flat
- Flat maps are scanned and digitized to create GIS Databases -Rasters are flat and its impossible to create a raster on a curved surface - The earth has to be projected to see all of it Much easier to measure distance on a flat surface |
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What are the two types of projections and what do they distort?
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- Equal area - distorts shape in order to preserve area
- Conformal - distorts area in order to preserve shape |
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What is a Line of tangency VS a line of secancy?
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A line of tangency is the same thing as a line of secancy. The only difference is a line of tangency is usually found on cylindrical projections and secancys are found on conic projections and usually come in twos
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The mercador Projection is what shape and kind of projection?
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- Cylindrical - Conformal (preserves shape but sacrifices area)
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What is the difference between a standard parallels and lines of secancy?
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Nothing.
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What are important conic projections?
What are they good for? |
- Labert Conformal Conic
- Albers Equal Area Conic - both good for long E-W extent and short N-S extent - One is good for shape and the other is good for area (its obvious which ones whcih) |
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What is an Azimuthal Projection? What is it used for?
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- Refereed to as Orthographic Projections
- Projected as a plane that either intersects the earth at a point on on a standard parallel. The points are graphed as if looking through the earth onto the plane - Used to accurately show a portion of the earth, or for artistic cartographic effect |
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How are points mapped on an unprojected projection?
What kind of projection is it? |
- all points are mapped as X, Y coordinates
- Cylindrical and neither conformal nor equal area, instead it is refered to as equidistant. - Lines of lat. are increasingly off as you move away from the equator. |
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What is the Transverse Mercator?
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- a Mercator projection that is instead uses lines of longitude as lines of tangency.
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What is UTM?
How does it work? |
- Universal Transverse Mercador.a set of 60 maps that divided every 6 degrees of longitude. Using this set of maps, equal area and shape are relatively well preserved.
- Must know what zone you are in. |
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How do the zones in a UTM map relate to one another?
What do you do if a feature spans multiple zones? |
- Each zone represents a new projection
- Sones will not line up on their common border - features that span more than one zone need to either only use one zone and accept the distortions or use a third projections that spans the zones. |
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What are state plane coordinates used for?
Who are they defined by? |
- high precision measurements such as surveying
- Defined by the state and each state often has multiple state plane coordinate systems. |
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What does converting georeferencing do?
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- takes placenames (addresses, streets, etc..) and converts them into coordinates using geocoding functions and gazetteers
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What is a data model?
- What model is best? |
Set of rules or constructs for representing real-world objects and their related processes in a digital environment
- No one model is best. |
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What are the stages of data modeling starting with the real world?
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- Real world --> GIS Data Model (despription and representation of real world) --> Opperation GIS (analysis and presentation of Data Model to optimize it for its application) --> People (interpretation and explanation of the GIS to answer questions)
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Why cant you skip from The GIS Data Model --> to --> people and skip operational GIS?
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Because no one data model is best for all people. Operational GIS adjusts the data model to display and represent the real world in the way that each group of people need it.
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What are the 4 layers of data modeling?
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- Reality (everything that your dealing with)
- Conceptual Model (real things that come into play i.e. manhole covers vs fire hydrants and noticing their differences) - Logical Model (How you will display the manhole covers for example) - Physical Model (bits of data used to tell the comp how to display the logical model u want) |
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The Raster/Grid Data Model is used for what?
What values matter? The TIN Data Model is used for what? What values matter? |
- Spatial anaysis and modeling
- Dont care about individual pixel value other than color - Surface/terrain analysis/modeling - care about value of pixel to answer question like where water will flow |
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Study Raster Topology reading rules.
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Yep you heard me!
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What is topology?
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the science and mathematics of geometric relationships.
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In relation to topology, define these terms in a context example:
- Connectivity - Adjacency - Containment |
- tracing a network of conncected pipelines or powerlines in order to figure out who gets power from where
- What properties share a common line as my focus property - What features are within the boundaries of my property |
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Topological Uses:
Three questions for Data Validation of polylines |
- Do all network elements conncect? (just because they cross does not mean they intersect i.e. small road and highways)
- Are there junctions as crossing polylines? - Do adjacent Polylines overlap? |
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Topological Uses: Two Questions for Modeling integrated behavior
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- neither road has traffic lights, instead the intersection does
- Common boundaries (states, counties) - Aggregation at network junctions |
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Topological Uses: Three points and a definition for Editing productivity
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- how can we increase the speed at which we edit the features
- manipulate common boundaries - Snapping - Auto-closure |
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Topological Uses: considerations for spatial analysis (3 uses of spatial analysis)
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- Network tracking
- Polygon adjacency - Intersection |
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Why is planar enforcement imperative for the working success of GIS?
- What two factors are required for planar enforcement |
- Without planar enforcement, GIS would not be capable of calculating area, shape etc..
- area must be mutually exclusive and collectively exhaustive |
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What does mutually exclusive mean?
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- This means no two polygons can contain the same area. If two polygons "you" see cross, the area that crosses is made into a different polygon
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What does Collectively Exhuastive mean?
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- The second rule of planar enforcement
- It means the sum of all of the polygon Must equal the area displayed. ArcMap makes any area that is not a polygon into a polygon but it doesn't show the viewer, then it adds them all together to get the sum area |
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Planar Enforcement:
- All ploygons must ____ - All lines in a network must be _____ - All polygons must be _______, whether the viewer seen it or not |
- Close
- Joined - Addressed |
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Review page 6 of Geographic data modeling
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No seriously, write that down and review it. Seriously tho, do it. Thanks.
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What shape does ArcMap use to map elevation and how does it work?
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- irregular triangles. If triangles are used then were is no confusion as to where or not there is an incline or a decline due to the angles of the triangle
- They also only have 1 aspect and 1 slope |
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What is aspect?
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a compass direction
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What is an object data model?
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- A data set that attaches attributes in a table to a point or a series of points to make a polygon on the earth's surface.
- they used to be two separate entities, now they are joined as one |
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What common mistakes happen when dealing with designing data modeling?
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- Designing the model seperately without referencing the GIS software core data model
- Not budgeting the right armount of time - Too generic and not specific and practical - Design for elegance instead of performance |
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What is one of the biggest drawbacks of data collection?
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Its expensive
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What are the two types of data collection? define them.
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- Data capture (you go out in the field with a GPS device or u use an arieal photo to create data)
- Data Transfer (obtaining data from a source that has already created it, usually requires modification) |
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What are the two broad capture methods of data capture?
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- Primary (direct measurement)
-- Raster: Remote sensing images or areial photos -- Vector: GPS or Surveying - Secondary (indirect derivation) -- Raster Scanned maps or Digital elevation models (DEMs) from maps -- Vector: Topographic surveys or toponomy (place names) data sets from atlases |
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What is a major part of the budget in a small GIS company that is not as big of a deal in a large GIS company?
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Collection of data. Because the cost of collecting any data is very high, but once you foot the bill for initiating data collection, it doesnt go very much higher from there. This is why data collection for a small firm is about as expensive for a big firm but a big firm has a bigger budget so staff much outweighs the cost instead.
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what are the 5 stages in data collection?
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- Planning
- Preparation - Digitizing/Transfer - Editing/improvement - Evaluation |
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What is the difference between a passive and active sensor?
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A passive sensor records light being emitted off the earth like in a photograph where as an active sensor emits a lazer beam or other form of energy and records what it receives back from that.
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What is the difference between Spatial, spectral and temporal resolution?
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- Spatial is the ability to resolve two lines that are close together
- Spectral is the ability to distinguish between two different colors - Temporal resolution is the time fram at which the picture is accurate (high temporal resolution would be every few minutes, low res. would be months or years) |
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How can reflective signatures predict crop yields?
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Different conditions of plants corresponds with different absorption of light thus a wilting plant will have a different signature than a healthy plant, thus crop yield foresight can be obtained
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What causes errors in GPS readings?
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- Atmosphere bends light at different pathlenth which slows it down.
- Interference from other signals - Obstructions from plants trees etc.. - Clock is not 100% accurate |
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What is differential correction and how does it work?
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- Corrects for atmospheric distortion by use of a tower that sends a terrestrial signal to certain GPS devices that have chips allowing them to connect
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What type of scanner is used to scan raster data sets?
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Either a scanner that has a fixed light and pulls the paper in or a drum scanner that uses a clear drum with the map taped to it. the light source is fixed and the drum moves forward and backward
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What is vectorization? whats the downside?
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The use of a computer application that draws vector lines in where the pixels of a raster data set is representing a line. Downside is that the vector lines that get drawn will not only be for features but also for numbers and letters drawn on the map which take a lot of time to delete
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What are the two types of digitizing?
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Manual- Using a very heavy table filled with copper and a scanner that draws the points on the computer (you cannot see what your drawing as you do it)
- Heads up (scanning and then tracing the map features on the map using computer software like AcrMap where you can see what you're drawing) |
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What is Photogrammertry?
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The science and technology of making measurments from photographs
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what does COGO stand for?
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Coordinate Geometry
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What are the two access technologies used in data transfer?
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- Translation (Copying data from a remote source)
- Direct read (Directly connecting to a source so that if a change in the database occurs, it will change in your dataset as well in near realtime) |
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Managing Data Capture Projects:
Key Principles |
- Clear plan, Adequete resources, Appropriate funding, and sufficiant time
- These almost never occur in perfect amounts, its all a compromise |
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Managing data Capture Projects:
What are the three fundamental tradeoffs? |
Quality, speed and price
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Managing Data Capture Projects:
What the two strategies used for capture? |
Incemental- where you go in phases because of either funding or because you dont know everything you need right from the start and this lowers bugdet and increases effency tho it also takes more time.
- Blitzkrieg (all at once which is quick but its very expensive all at once and there are lots of opportunities for errors) |
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Why is it very very important to catch errors before they are put into a database?
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- because they are very very difficult to spot once they are in the data, especially with a lot of data.
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What is a database?
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an integrated set of data on a particular subject (a filing cabinet is even a database)
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What is a geographic database?
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- geographic data of a particular subject for a particular area (database containing spatial data)
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What is a Database Management System (DBMS)
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- software to create maintain and access databases (software that creates and stores data)
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What are the advantages of databases over files
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- avoids redundancy and duplication
- Reduces maintenance cost of data - easier data sharing - security is much easier to define and enforce - can support many different applications |
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What are the disadvantages of databases over files
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- Expensive if only for a small amount of data
- Can be very complex - Performance slows with very large datasets - Integration with foreign systems can be difficult |
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Types of DataBase Management System (DBMS):
Hierarchial |
- States contain counties which contain tracts which contain block types which contain blocks
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Types of DataBase Management System (DBMS):
Network |
- based off of connectivity or links
- point A, B and C are connected by Lines 1, 2 and 3. each line and point has some attribute as well |
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Types of DataBase Management System (DBMS):
Relational (RDBMS) |
- essentially lists of tables that can be linked or related together
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Types of DataBase Management System (DBMS):
-Object-Oriented (OODBMS) - Object-relational (ORDBMS) |
- objects with attributes that are on separate lists and cannot be joined
- Objects with tables that can be joined and related together and with other tables |
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What does SQL stand for?
What kind of databases do they solve queries for? |
- Standard Query Language
- Relational Databases |
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Who Developed SQL?
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IBM in the 1970s
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What are the three types of usages of an SQL statement?
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- Standalone Queries
- High level programming - Embedded in other applications |
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Characteristics of DBMS:
What does it mean when it says "data model can support multiple data types? |
- it means the data can be in many different formats and the program is capable of recognizing it as such, for example date, time, number, text, currency etc..
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Characteristics of DBMS:
Where can you load data from? |
- files, other databases or other applications
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Characteristics of DBMS:
What does indexing do and why is it beneficial? |
- Indexing organizes the data in a chosen way which allows the computer to find and retrieve data faster
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Characteristics of DBMS:
What is the Query Language? |
- SQL
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Characteristics of DBMS:
What controls the updates of a database? |
- Transaction manager (program/application)
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Characteristics of DBMS:
What are 4 applications of DBMS? |
- CASE tools
- Forms builder - Reportwriter - Internet Application Server |
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Characteristics of DBMS:
Look at page 4 of the slide set 'creating and maintaining geographic databses' |
- Ok run along now, Git!
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Relational Databases:
What two formats is the data stored as? |
- tuples which is conceptualized as a table. Its a series of numbers in parentheses that is attached to a piece of data and acts as a coordinate system to identify datas location in a table
- Tables, the structured arrangement of data with rows (objects) and columns (properties/attributes) |
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Relational DBMS:
What percent of data found in DBMS is found in RDBMS? - What commercial systems are offered in RDBMS? |
- 95%
- IBM DB2 - Informix - Microsoft Access - Microsoft SQL Server - Oracle - Sybase |
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Relational Databases:
What relational rules govern the 'perfect table?' who defined them? |
- Developed by Ted Codd of IBM in 1970
- Rules: only one value in each cell - each row is unique - no significance in column or row sequence |
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Relational Databases:
When a table follows Codd's relational rules what is the table known as? |
- Normalized, the process of converting is known as normalization
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Relational Databases:
What does a normalized table allow? (relational join, forms) when is it ok to denormalize? |
- Allows tables to be split into new tables that can be joined at query time (relational join)
- normaized in to many levels or (forms) 1NF, 2NF, 3NF etc - Normalizing created many computationally expensive joins - it is ok to denormalize when attempting to optimize performance |
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Relational Databases:
What is a relational join? Why does it occur? What does it need to occur? |
- a fundemental query operation that bring two pieces of data in tables to together using a common field
- occurs because of normalization, and because data is created and maintainbed by different users but intergration is needed for queries - A common field is needed in order to successfully join the fields |
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What is spatial analysis?
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- Turns raw data into useful informations by reviealing patterns, treands and anomalies that may be missed by human intuition because the human eye and brain can sometimes deceive
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How can we define whether an object is in need of spatial analysis?
What two aspects does spatial analysis require to function? |
- If you move the objects and the results change then spatial analysis is needed for that object/s
- Both attributes and the location of objects |
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Who is Dr. John Snow and how did he use spatial analysis?
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- Dr. John snow was a medical Dr. in the 1850s in London where cholera broke out. He suspected drinking water was the culprit and found that all the cases centered around a central well. He had the handle removed and the outbreak subsided.
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Using spatial analysis, how would GIS be used to map a contagion or drinking water outbreak?
What would each look like? |
- A sequence of maps would be made to attempt to determine the patter of outbreaks by location
- If contagion (airborne) then it would be a series of concentric circle - If water based ailment, then it would be of a more random sequence |
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Six categories of spatial analysis used in this course?
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-queries and reasoning
- Measurements - Transformations - Descriptive summaries - Optimization - Hypothesis testing |
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Six Categories of Spatial Analysis:
Queries and reasoning, how does a GIS respond to queries? How is this response used? What is this technique called? |
- A GIS will create different views with the data and the viewer can interact with the views
- More than one view can be used at once and they can be linked together - This is called Exploratory Spatial Analysis (ESDA) |
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Six Categories of Spatial Analysis:
Why are Measurements important when using GIS? Why is GIS a great candidate for carrying this out? |
- Many tasks such as distance between two points, direction and area are very useful to know.
- Measurments made by hand can be inaccurate and slow, GIS is fast reliable and accurate |
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Six Categories of Spatial Analysis: Measurements:
- What is a metric? - What is the Pythatgorean Metric? - What is the Great Circle Metric? |
- a rule for determining distance between two points
- a metric for determining distance between two points on a flat surface - a metric for measuring the distance between two points on a spherical globe given lat. and long. |
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Six Categories of Spatial Analysis: Measurment:
How the comp measures area of an irregular circular object. |
- by comparing perimiter to the square root of the area, you can identify how contorted from a circle it is. A circle is normalized to equal 1 so the further from 1, the more contorted that shape.
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Six Categories of Spatial Analysis: Measurement:
How does the GIS measure slope and aspect? |
- calculated from a grid of elevations (DEM)
- slope and elevation are calculated by comparing its 8 neighbors to itself using irregular triangles - it is important do document how slope is calculated and how it is defined because it can vary from method to method |
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Look over slide 18 or chapter 14.
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K thanks bye.
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Types of Spatial Analysis: What is transformation?
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- the construction and calculation of geometric objects.
- may also create new fields from existing fields from discrete objects |
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What is buffering and what type of spatial Analysis is it part of?
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- buffering is creating polygons consisting of areas representing a specified distance away from a chosen polygon
- This is a for of transformation |
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How is raster buffering carried out?
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- it uses a value in each cell that represents the variable you are trying to identify. With this it can deterine a variable response distance using a friction layer that calculates distance as a function of the value in the cell (in the example of response distance the value is time)
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How does the computer determine whether a point is inside or outside of a polygon?
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- from the point it draws an infinite line in any direction and lists the number of times the line crosses each polygons sides. The polygon with an odd number of crosses is the polygon containing the point.
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How does the computer compute polygon overlay, or two polygons occupying the same area?
what are the attributes said to be? is this task often performed in raster or vector? |
It make a new layer that has both attribute of the polygons in the attribute table and lists whether they are present in each polygon or not.
- The attributes are said to be concatenated - often performed in raster |
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What is a sliver polygon, how it it created and how is it dealt with?
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- a sliver polygon is created when two features share a common boundary like a river and a property line but these are viewed at two separate polygons that don't exactly line up.
- this is dealt with using tolerances |
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What is Inverse Distance Weighting (IDW)?
how does it work? |
- basically its a way of estimating the values in a field that have not been measured
- it averages all the surrounding values and assigns higher weights to the values closest to the point |
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What is IDW formula?
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z(x) = (SUM w*z points)/ (SUM w point values)
where: w=weight=1/d^2 d=distance from central point z=known value of points |
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Issues with IDW (Inverse Distance Weighting)
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- the range of estimated interpolated values cannot exceed the range of observed values
- must include the sample points and location of the highest values of the field - this can be very difficult |
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If interpolation of a mountain peak is attempted, what is a possible undesierable characteristic?
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- the value for the peak will not be higher that the last two observed points, instead it will be lower in order to try to meet the mean of all of the points which leaves the mountain peak either flat or concaved like a volcano.
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