Gis Test 1

Front 1

GIS

Back 1

Software, hardware, data, people, methods

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Functions of GIS

Back 2

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

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Maps concerned with two elements of reality:

Back 3

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

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Maps are:

Back 4

A system of layers

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Layers

Back 5

contain features

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features

Back 6

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

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vector data

Back 7

polygon, line, point

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cartography

Back 8

making and study of maps in all their aspects

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Principles of map design

Back 9

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

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map composition

Back 10

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

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map body

Back 11

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

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When you would use an inset map

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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

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Visual hierarchy

Back 13

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

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balance

Back 14

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

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contrast

Back 15

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

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3 approximations of earth

Back 16

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

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use of sphere

Back 17

small scale maps, countries, continents

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use of ellipsoid

Back 18

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

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use of geoid

Back 19

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

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Coordinate system

Back 20

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 (3-D or 2-D), unit of measurement, the definition of the map projection for projected coordinate systems

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two types of coordinate systems used in GIS

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1) geographic coordinate systems and 2) projected coordinate systems

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***geographic coordinate systems (or GRATICULE)

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

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projected coordinate systems

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

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Developable surface

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

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Class

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

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3 common classes

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cylindrical, conic, planar

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cylindrical characteristics

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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

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conic characteristics

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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; "pie-wedge" shape; the angular extent of the wedge, and the spacing of the parallels distinguish one conic projection from another

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planar characteristics

Back 29

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

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case

Back 30

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

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aspect

Back 31

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

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Datum

Back 32

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

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Distortion

Back 33

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

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Distortion – How do we Analyze it ?

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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)

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Scale

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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

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Scale Factor in Action

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

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FOUR Spatial Relationships that can be
preserved or distorted by a particular map
projection

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Relationship (Projection)
• Area (Equivalent, or Equal Area)
• Angle (Shape) (Conformal)
• Distance (Equidistant)
• Direction (Azimuthal Projections)

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Equivalent Projections (or, Equal Area)

Back 38

Preservation of Area, mollweide (cylindrical)

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Conformal Projections

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Preservation of Angular Relationships, Mercator

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Equidistant Projections

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Preservation of Distance Relationships

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Azimuthal Projections

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Preservation of Direction

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Choosing the Correct Map Projection: pearson's guidelines

Back 42

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

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Choosing correct map projection: robinson's guidelines

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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

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Grid Systems

Back 44

• 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

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Thematic Mapping

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• 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

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Spatial Distribution

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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

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Data Measurement

Back 47

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, non-arbitrary zero)

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Thematic Mapping Techniques

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Choropleth
• Proportional Symbol
• Isarithmic
• Dot Mapping

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Choropleth Mapping

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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

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Proportional Symbol

Back 50

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

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Isopleth/Isarthmic Mapping

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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

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Dot Mapping

Back 52

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

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Data Classification

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

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Equal Intervals

Back 54

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

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Quantiles

Back 55

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

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Natural Breaks

Back 56

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

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Mean – Standard Deviation

Back 57

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

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Geometrical Interval

Back 58

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

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representative fraction

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

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map projection techniques

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

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model

Back 61

an idealized and simplified representation of reality

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what is a model?

Back 62

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

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data model

Back 63

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

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spatial data model

Back 64

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

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what's the use of spatial modeling?

Back 65

-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

Front 66

vector data model

Back 66

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 pairs-nodes) and detailed (multiple pairs - nodes & vertices)
-polygon: set of connected line segments, with the same start/end point

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vector data

Back 67

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

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spaghetti vector model

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-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

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topological vector model

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

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topology

Back 70

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

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topological relationships

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

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typical topological relationship

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

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intra-layer relationships

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-overlap and connectivity

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raster

Back 74

-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

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raster data model

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-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

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vector advantages and disadvantages

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+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

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raster + and -

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+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)

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advanced model: digital elevation model

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

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advanced data model:network model

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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

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advanced modeling: object data modeling

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

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simplified modeling process for problem solving

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-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

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map projection

Back 82

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

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tangent v. secant

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-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

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tissot's indicatrix

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-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