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84 Cards in this Set

  • Front
  • Back
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
contain 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
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
refers to the organization of map elements and the empty space, resulting in visual harmony and equilibrium
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 (3-D or 2-D), 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 2-d cartesian coordinate plane
Developable surface
a mathematically definable surface onto which the land masses and graticule are projected from the reference globe
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; "pie-wedge" 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
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
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
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 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 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
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
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, non-arbitrary zero)
Thematic Mapping Techniques
• 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)
 Doesn’t show variation WITHIN mapping unit
 Based on arbitrary boundaries
 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
 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
 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
 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. Mean-Standard 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
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
• Advantages
– Considers how data are distributed
along the number line
– If data are normally distributed,
then the Mean is a natural dividing
• 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
– Produces a result that is visually
appealing and cartographically
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
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 pairs-nodes) 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
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)
-non-planar (overlaps allowed)
intra-layer relationships
-overlap and connectivity
-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 3-d locational data (your location in the real world) onto the 2-d 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