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84 Cards in this Set
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GIS

Software, hardware, data, people, methods


Functions of GIS

Identify location, ID distributions, relationships, and trends, integrate data, combine & overlay data to solve spatial problems, map can model future events


Maps concerned with two elements of reality:

locations (positions in two dimensional space) and attributes (qualities or quantities, such as city names or pop figures)


Maps are:

A system of layers


Layers

contain features


features

can take form as vector data and each feature is linked toa row of info in the attribute table


vector data

polygon, line, point


cartography

making and study of maps in all their aspects


Principles of map design

purpose, geographic space/expanse (reality), available data, map scale, audience, conditions of use, technical limits


map composition

map body, inset/overview map, title, legend, scale, direction indicator, map metadata


map body

geographical reference  base info; contect  floating or cropped; positioning  right, left centered; zoom  give the study area room to breathe


When you would use an inset map

to show a primary map area in relation to a larger more recognizable area; to enlarge important or congested areas; to show alternate thematic topics that are related to the maps theme, or different dates of the same theme


Visual hierarchy

refers to the order of the graphical representation of your map info


balance

refers to the organization of map elements and the empty space, resulting in visual harmony and equilibrium


contrast

refers to the visual differences between map features that allow ust o distinguish one feature from another...can be implemented through: spacing, size, perspective height, orientation, shape, arrangement, all aspects of COLOR


3 approximations of earth

sphere, ellipsoid, geoid (the colorful, trippy looking one)


use of sphere

small scale maps, countries, continents


use of ellipsoid

large scale maps of smaller areas
mathematically predictable, one of the best models to use 

use of geoid

reference surface for ground surveying of horizontal and vertical positions
maps gravitational anomalies of earth's surface...where gravitational forces differ 

Coordinate system

a ****reference system used to represent the locations of geographic features, imagery, and observations such as GPS locations within a common geographic framework...each system is defined by: measure framework (3D or 2D), unit of measurement, the definition of the map projection for projected coordinate systems


two types of coordinate systems used in GIS

1) geographic coordinate systems and 2) projected coordinate systems


***geographic coordinate systems (or GRATICULE)

global or spherical coordinate system such as LATITUDE OR LONGITUDE, typically expressed as Degree Minute Seconds or Decimal Degrees


projected coordinate systems

coordinate system that provides various methods to project the earth's spherical surface onto a 2d cartesian coordinate plane


Developable surface

a mathematically definable surface onto which the land masses and graticule are projected from the reference globe


Class

refers to overall appearance of the graticule, once the projection process is complete


3 common classes

cylindrical, conic, planar


cylindrical characteristics

lines of longitude are straight, equally spaced; lines of latitude are straight, parallel and intersect lines of long at right angles; the spacing of the parallels distinguishes one type of cylindrical projection from another


conic characteristics

lines of longitude are straight lines of equal length, radiating from acentral point (poles); lines of latitude are concentric circular arcs centeres around one of the poles; "piewedge" shape; the angular extent of the wedge, and the spacing of the parallels distinguish one conic projection from another


planar characteristics

lines of longitude are straight, equally spaced, parallel lines that radiate from the cneter; linesof latitude appear as equally space concentric circles, centered about a point; again, the spacing of the parallels distinguishes one type of planar projection from another


case

the case of a projectionr elates to how the developable surface is positioned with respect to the reference glove...can be described as tangent or secant
effects distortion by shrinking middle and enlarging the ends 

aspect

The Aspect of a Projection deals with the
placement of then projections center with respect to the earth’s surface A projection can have one of three aspects: 1. Equatorial 2. Polar 3.Oblique 

Datum

Every Geographic Coordinate System includes an angular
unit of measure, a prime meridian, and a datum • A datum defines the position of the spheroid relative to the center of the earth 

Distortion

Distortion is altering the size or shape of the
earth’s landmasses and graticule for projection to a flat or planar surface 

Distortion – How do we Analyze it ?

Scale Factor (numerical assessment of how the map scale at a specific map
location compares to the map scale at the a standard point, or along a standard line) Scale Factor = Local (Map) Scale/ Principle Scale Local Scale – The Scale computed at a specific location Principle Scale – The Scale computed along the Standard Line or Point (true scale) 

Scale

Scale is the ratio of map units to earth units, with the map
units standardized to 1 • 1:100,000 • 1:25,000 Scale is a UNITLESS measure – To Calculate • Scale = Map Distance / Earth Distance Do not confuse Scale with Scale Factor 

Scale Factor in Action

Scale Factor = Local Scale (Measured from Map)/
Principle Scale (Real World Measurement) 

FOUR Spatial Relationships that can be
preserved or distorted by a particular map projection 
Relationship (Projection)
• Area (Equivalent, or Equal Area) • Angle (Shape) (Conformal) • Distance (Equidistant) • Direction (Azimuthal Projections) 

Equivalent Projections (or, Equal Area)

Preservation of Area, mollweide (cylindrical)


Conformal Projections

Preservation of Angular Relationships, Mercator


Equidistant Projections

Preservation of Distance Relationships


Azimuthal Projections

Preservation of Direction


Choosing the Correct Map Projection: pearson's guidelines

Pearson’s Guidelines (Based on Latitude/Class)
Equatorial Regions (0° to 30° N/S) – Cylindrical Mid Latitude (30°  65° N/S) – Conic Polar Regions (Above 65°) – Planar 

Choosing correct map projection: robinson's guidelines

Robinson’s Guidelines (Based on Function/Properties)
Conformal – Analyzing, measuring, recording angular relationships. Use for navigation, piloting, surveying Equivalent – Geographic comparisons across space. Use for thematic maps that represent proportions, either through color, or dot density Planar – Tracking the direction of movement Equidistant – Determination of distances 

Grid Systems

• Stated simply – a grid placed over a map projection using a plane or
Cartesian (x,y) coordinate system to locate features • Created for larger scale mapping • Divided into zones with only positive coordinate numbers (metres or feet) • Easier to calculate area, direction and distance • Universal Transverse Mercator (UTM) and State Plane Coordinate System 

Thematic Mapping

• A thematic map shows the spatial distribution of one or
more specific data themes for standard geographic areas • Thematic maps can portray physical, social, political, cultural, economic, sociological, agricultural, or any other aspects of a city, state, region, nation, or continen 

Spatial Distribution

This is the arrangement (spread, pattern), of thematic
phenomena in geographic space • Geographic Phenomena can be arranged along the following lines: • Discrete • Continuous • Abrupt • Smooth 

Data Measurement

Levels of Measurement
Qualitative Data 1. Nominal (Categorization) Quantitative Data 2. Ordinal* (Categorization & Ordering) 3. Interval (Ordering & Explicit Values, arbitrary zero) 4. Ratio (Ordering & Explicit Values, nonarbitrary zero) 

Thematic Mapping Techniques

Choropleth
• Proportional Symbol • Isarithmic • Dot Mapping 

Choropleth Mapping

Used to portray data collected for Enumeration Units
Suited to: Abrupt Data Typical Values (such as averages for certain figures or population densities) Disadvantages: Doesn’t show variation WITHIN mapping unit Based on arbitrary boundaries Considerations Standardization of Data Unevenly sized Enumeration Units 

Proportional Symbol

Scaling Symbols in proportion to the magnitude of the data around a
central point. Can be used for actual or conceptual points. Suited to: Raw Data Totals Disadvantages: Can become crowded on maps with small enumeration units 

Isopleth/Isarthmic Mapping

An Isarthmic map (contour map) is created by interpolating a set of
isolines between sample points of known values (example – contour map) An Isopleth map, is a special kind of isarthmic map in which the sample points are associated with enumeration units Suited to: Smooth Data Totals Considerations Standardization of Data Finer level of enumeration units more suitable 

Dot Mapping

In dot mapping, one dot is set to be equal to a certain amount of
phenomena, and ideally the dots are placed where that phenomena are most likely to occur Suited to: Raw Data Totals Disadvantages: If you do not have access to ancillary information, such as satellite imagery, it is hard to have confidence in dot placement 

Data Classification

1. Equal Intervals
2. Quantiles 3. Natural Breaks 4. MeanStandard Deviation 5. Optimal 6. Manual 7. Geometrical Interval 

Equal Intervals

Divides the range of
attribute values into equalsized sub ranges • Advantages – Easy Calculation – Easy Interpretation – No Gaps • Disadvantages – Does not consider data distribution along the number line 

Quantiles

Equal numbers of
observations are placed in each class • Advantages – Easy (manual) Calculation – Allows use of the complete color spectrum • Disadvantages – Identical Data values MAY be placed in different classes – Again, fails to consider how data is distribution along the number line 

Natural Breaks

Classes are based on natural
groupings inherent in the data through examination of the histogram • Advantages – Minimizes the differences between data values in the same class & maximize the differences between classes • Disadvantages – Data ranges are usually uneven 

Mean – Standard Deviation

This classification scheme shows
you how much a feature's attribute value varies from the mean. • Advantages – Considers how data are distributed along the number line – If data are normally distributed, then the Mean is a natural dividing point • Disadvantages – ONLY works well for data that are normally distributed 

Geometrical Interval

This is a classification scheme
where the class breaks are based on class intervals that have a geometrical series. – An algorithm creates these geometrical intervals by minimizing the square sum of elements per class – Ensures that each class range has approximately the same number of values with each class and that the change between intervals is fairly consistent. – Produces a result that is visually appealing and cartographically comprehensive 

representative fraction

the ratio of map distance to earth distance, and indicates the extent to which a geographic region has been reduced from its actual size


map projection techniques

1. reduce the earth's size to that of an imaginary globe
2. project the graticule from the reference globe onto the developable surface 

model

an idealized and simplified representation of reality


what is a model?

a globe is a model of the earth...a map is a graphical model of the earth surface


data model

set of constructs for representing objects and processes in the digital environment


spatial data model

a set of constructs for representing geographical objects, data, processes, and relationships in the digital environment, for the purposes of analysis and complex problem solving


what's the use of spatial modeling?

finding relationships among geographic features to understand and address any particular problem
it provides a framework for understanding real world processes it can facilitate the extraction of info that is either impossible or too expensive to measure in the real world allows you to qualify info clearly 

vector data model

a method of storing, representing or displaying spatial data in digital form. it consists of using coordinate pairs (x.y) to represent locations of the earth. features can take th eform of single points, lines, arcs, or closed lines.....
point: single coordinate pair lines: simple (set of coordinate pairsnodes) and detailed (multiple pairs  nodes & vertices) polygon: set of connected line segments, with the same start/end point 

vector data

building block of GIS...basic way to represent something (through point, lines, and polygons)


spaghetti vector model

more of a lack of model
when cartography first emerged, people just drew lines...therew as no notion of connectivity or notion of spatial relationships 

topological vector model

data is more carefully constructed
rules set up to address shortcomings of spaghetti vector there is strict connectivity and adjacency, rules enforced 

topology

the mathematics and science of geometrical relationships used to validate the geometry of vector entities


topological relationships

the properties of geographic objects that do not change when the forms are bent, stretched, or undergo similar transformations


typical topological relationship

connectivity and directionality (lines)
adjacency and exhaustive (polygon) planar topology (no overlaps) nonplanar (overlaps allowed) dangles 

intralayer relationships

overlap and connectivity


raster

a method of storing, representing or displaying spatial data in digital form
used more commonly to show continuous data you can show changes more subtly because you make variations within geographic unit 

raster data model

cell dimension: resolution of raster cell (length & width in surface units)
level of detail  number of cells decreases dramatically as image gets bigger (comparatively) spatial precison: assume that it is no better than 1/2 of cell dimension: because raster data is harder to be confident in the level of accuracy (hard to pinpoint center, for example) ~positional accuracy is assumed to be no better than one half of the cell size data assignment ~point physical value: taking a point reading within a physical cell ~statistical value: averages, percentages (not necessarily always physical attribute) ~classification data: identification ~point/line/polygon reassignment: taking vector data and turning it into raster...the cell takes on the attributes of the line within cell variation 

vector advantages and disadvantages

+vector is capable of being most precise
+vector data is just numbers so it is easier to store a lot more detail in a lot smaller space +quality of cartographic output certain types of apatial analysis does not work on vector data 

raster + and 

+ability to store and represent large amounts of info (detail)
file size (and draw time) due to the large amount of data being stored lack advanced data structure characteristics (topology, network analysis) 

advanced model: digital elevation model

DEM: geographic data that represents elevation (vector or raster)


advanced data model:network model

it is a system of interconnecting elements consisting of lines (often called edges) in a network and points. represent possible routes from one location to another
shortest path is most common route geometric: generally utility networks difference in geometric v transportation…in geometric, stuff only travels in one direction at one given time. whereas in transportation, travel can be in both directions and its generally person in vehicle that decides where they're going 

advanced modeling: object data modeling

the key behind object data modeling is to look at a collection of geographic objecst and the relationship between those objects


simplified modeling process for problem solving

ID problem
breakdown the problem organize data required to solve the problem develop a clear and logical flowchart using well defined operations run the model and modify it if necessary 

map projection

a method/process that involves the mathematical transformation of 3d locational data (your location in the real world) onto the 2d plane (or flat surface)


tangent v. secant

tangent versions are mathematically simpler but overall there's more distortion on the map (only one point of contact)
secant: two points of contact so it is a bit more mathematically challenging but is more reliable 

tissot's indicatrix

indicates ways distortion can happen on a map
B is angular distortion but aerial preservation C is a change in axes A&B but it is uniform…the angle doesn't get affected but area is different D…everything is different 