Introduction to Geographic Information Systems

More Map Basics

• "A graphic depiction of all or part of a geographic realm in which the real-world features have been replaced by symbols in their correct spatial location at a reduced scale."

• Storage
• Temporary communication
• Intermediate check of data
• Final Report
  • to be effective, must be correctly designed and constructed

• production of a map requires:
  • selection of a few real-world features to include
  • classification of selected features into groups (i.e. bridges, churches, railways)
  • simplification of jagged lines like coastlines
  • exaggeration of features to be included that are too small to show at the scale of the map
  • symbolization to represent the different classes of features chosen

• Cartographers make 4 crucial decisions when constructing a map:
  • map projection
  • selectivity
  • map type
  • map scale

• See the previous lecture for details on map projections

• a map offers a selective and distorted view of reality due to the cartographer's decisions related to the map's ultimate use
• maps:
  • include information only selectively
  • exclude much information that exists
  • distort information

• Cartographers have designed hundreds of map types: methods of cartographic representation.
• Not all GISs allow all types.
• Most have a set of basic types
• Depends heavily on the dimension of the data to be shown in the map figure.

• Fairly common GIS error.
• Due to lack of knowledge about cartographic options.
• Can still have perfect symbolization.
• Possibility of misinformation
• Definite reduction in communication effectiveness.

• in practice, there are two fundamental types of maps:
  • reference map
  • thematic map
• the distinction between these two classes is based on map function

• a reference tool, showing the outlines of selected natural and man-made features of the Earth
• examples:
  • topographic maps
  • orthophoto maps
  • bathymetric maps
  • road maps

• a tool to communicate discrete geographical concepts and distributions
• examples:
  • population density
  • climate
  • movement of goods
  • land use, etc.
  • ethnicity

• several types of maps are important to GIS, each using a principal map symbol

  -choropleth	(area symbol)
  -area class	(area symbol)
  -dot	(point symbol)
  -proportional symbol	(point symbol)
  -isoline	(line symbol)
  -flow	(line symbol)

• a common type of areal quantitative map
• uses "reporting zones" to show data such as average incomes, percent female, etc.
  • countries, states, counties, census tracts, etc.
• boundaries of zones are established independently and may be used to report many different sets of data

• an areal map showing nominal distributions of phenomena
• shows zones of constant attributes, such as vegetation, soil type, or forest species
• zonal boundaries are different for each map since they derive from variations in the attribute being mapped (though they may be similar for related attributes)

• usually a quantitative map showing the distribution of an attribute by uniform dots
• used for mapping point and point-like data, such as population, livestock, radio stations, farm acreage, etc.
• map readability is affected by the size and number of dots on the map
• symbols may be any point-like graphic

• a quantitative map showing the distribution of an attribute by variably sized symbols
• similar to dot maps in mapping point and point-like attribute data like population, production levels, petroleum imports, etc.
• symbols may be any scalable, point-like graphic

• a map showing a surface by means of lines joining points of equal value--"isolines"
• used for phenomena which vary more or less smoothly across the map (a "statistical surface")
• isometric: values that occur at points
  • temperature, barometric pressure, rainfall
  • elevation (contour lines on a topographic map)
• isoplethic: values that don't occur at points
  • population density, ratio of cropland to all farmland

• a quantitative map showing connections, flows, or movements between locations
• examples: petroleum exports, migrations, river discharges, traffic volume
• quantitative values are usually shown by varying the width of the line or arrow showing the direction of movement

• Reference
• Topographic
• Dot
• Picture Symbol
• Graduated Symbol

• Network
• Flow
• Isopleth
• Reference

• Choropleth
• Area qualitative
• Stepped surface
• Hypsometric
• Dasymetric
• Reference

• [Isopleth, Stepped Surface, Hypsometric]
• Gridded fishnet
• Realistic perspective
• Hill-shaded
• Image map

• Multiple views
• Animation
  • Moving map
  • Fly thru
  • Fly by

• the ratio between distances on the map and corresponding distances in the real world
  • if a map has a scale of 1:50,000, then 1 cm on the map equals 50,000 cm on the Earth
• remember "small" vs. "large"
• the scale controls not only how features are shown, but what features are shown
  • a 1:2,500 map will show individual houses and lamp posts while a 1:100,000 map will not

• representative fraction (rf)
  • literally a ratio or fraction
• graphic
  • line or bar graph whose length represents a specified distance on the Earth
• verbal
  • a simplified description of map distance, such as "one inch equals one mile"

• Map scale is based on the representative fraction, the ratio of a distance on the map to the same distance on the ground.
• Most maps in GIS fall between 1:1 million and 1:1000.
• A GIS is scaleless because maps can be enlarged and reduced and plotted at many scales other than that of the original data.
• To compare or edge-match maps in a GIS, both maps MUST be at the same scale and have the same extent.
• The metric system is far easier to use for GIS work.

• refers to the size of the geographic units under investigation
  • cities, counties, states, countries, etc.
• a pattern evident at one level may not be evident at another
  • is the U.S. population becoming more concentrated?
  • at the larger metropolitan level, yes
  • at the smaller intra-metropolitan level, no

• Figure
• Ground
• Reference information
• Border
• Neatline
• Metadata e.g. index
• Off-map references
• Page coordinates
• Graticule/Grid
• North arrow
• Figure
• Point/Line/Area symbols
• Text
• Place Names
• Title
• Scale
• Projection(s)
• Sources/Credits
• Legend
• Insets and their scales

• Map research
• Map compilation
• Worksheet
• Selection
• Placement
• Layout
• Tools in GIS not ideal

• Check the data
  • Continuous
  • Discrete
  • Accuracy & Precision
  • Reliability
• Dimension (Point, Line, Area, Volume)
• Scale of Measurment (Nominal etc.)
• GIS capability
• May need to supplement GIS software

• Data should be AREA (e.g. states, counties, census tracts)
• Data should not suffer from area effect
• Data should be suitable quantitative value
• Data should be normalized
  • divided by, say, the total population or area
• Examples:
  • Population density
  • Per capita income
  • Deaths per 1000 people

• Equal Interval
• Natural groups
• N-tiles
• Equal or unequal?
• Logarithmic? Linear? Discontinuous?
• How many classes?
• Non-overlapping, distinctive groups

  

• To appear professional and avoid errors, GIS maps should reflect cartographic knowledge about map design.
• A map has a visual grammar or structure that must be understood and used if the best map design is desired.
• Cartographic convention (e.g. forests should be green).

• A GIS map is designed in a process called the design loop.
• Good map design requires that map elements be placed in a balanced arrangement within the neat line.

• Create map layout as macro
• Draw on screen (proof plot)
• Look
• Edit macro
• Repeat until happy
• Make final plot

• Vector
  • Adobe Illustrator
  • CorelDraw
  • Freehand
• Raster
  • Photoshop
  • CorelPaint
  • Fractal Paint

• Visual balance is affected by:
  • the "weight" of the symbols
  • the visual hierarchy of the symbols and elements
  • the location of the elements with respect to each other and the visual center of the map

• Smaller scale means fewer features.
• Smaller scale means smoother features.
• Smaller scale means combining features.
• Smaller scale means displacing features.
• Often scales are mixed or overgeneralized.

• When a GIS map is the result of a complex analytical or modeling process, good design is essential for understanding.
• The map is what distinguishes GIS as a different approach to the management of information, so extra care should be taken to improve the final maps that a GIS generates in a GIS task.

• You must consider the objective of the graphic display your map represents
• This involves visualization
  • process for putting (complex) images into the viewer's mind
  • examples:
    • the shape of a mountain - poorly conveyed by contours
    • pattern of growth of an urban area - may need animation to show changes through time effectively
    • air-flows over a patch of terrain - needs 3-D capabilities plus animation to show true pattern of directions, speeds of flow
    • movements of people in an area - needs ability to generalize individual movements into meaningful aggregate patterns
  • components of a visualization system:
    • database containing information
    • hardware device used to generate display
    • human visual system
    • processing of perceived image in the brain
  • correct perception depends on the functioning of all of these components

• what impressions does the analyst wish to create in the mind of the viewer?
• what relationship do these intended impressions have with the contents of the database?
  • database contents are abstract versions of geographical reality
  • the system should create an impression of reality, not of the contents of the database
  • aspects of relationship between database and reality, e.g. accuracy, should be an important part of the display
• geography is complex
  • the display is a filter removing unwanted complexity to show trends, patterns
  • the display must show the level of detail required by user, from a general overview to detailed insights

• effective visualization may require familiarity with symbols on the part of the user
  • some people may never master skills of map-reading, i.e. using maps to visualize geography
• how much familiarity should be assumed?
  • it may generally be better to assume low familiarity
  • people can learn to work with complex displays, but may lose interest and look for alternative sources of information

• communicates intended message perfectly to all users
  • is not mis-understood
• offers complete design flexibility
  • put any symbol anywhere, at any size, etc.

• classes of symbols correspond to classes of objects
  • point
  • line
  • area
• visual differences among map symbols convey information

• where the symbol is
• determined primarily by geography
• the primary means of showing spatial relations
• the brain computes relations like "is within" or "crosses" on the fly from the eye's perceived image of the map
• compare GISs
  • some compute these relationships on the fly, others store them in the database to avoid the processing required to compute them
  • compared to the brain, current GIS technology is amazingly crude

• lightness or darkness of a symbol
• very important visually -- the eye tends to be led by patterns of light and dark
• usually used to represent quantitative differences
• tradition suggests darker symbols should mean "more" -- however this may reverse on dark backgrounds (which are common on computer displays) where lighter may mean "more"

• color
• important aesthetically
• usually represents qualitative differences -- continuous grading of color is difficult and expensive to achieve on printed maps

• how large the symbol is
• conveys quantitative difference
• brain has difficulty inferring quantity accurately from the size of a symbol
  • if proportional circles are used to portray city population, doubling the radius of a circle (quadrupling its area) is perceived as indicating more than twice the population, but not four times
  • i.e. the brain infers population from some mixture of the radius and the area of the symbol

• geometric form of the symbol
• used to differentiate between object classes
• used to convey nature of the attribute, e.g. population indicated by images of people, housing by house symbols

• arrangement, density of symbols in a pattern
• used to show quantitative differences, e.g. dot density to show population

• of a pattern, to show qualitative differences
• of a linear symbol, to show quantitative (directional) differences

• symbol differences must be perceptible to be of use
  • JND -- just noticeable difference -- the smallest difference which can be reliably perceived between symbols, sizes, colors, shapes etc.
  • LPD -- least practical difference -- the smallest difference which can be produced by the cartographic process
• eye's sensitivity to various graphic codes
  • some codes "get through" better
  • e.g. use of yellow for fire trucks allows them to stand out better in the visual field
• sensitivity varies across visual field
  • "peripheral vision" is enhanced by movement, varies among individuals
• cognitive aspects
  • indications that perception is dependent on cognition -- knowledge understanding of phenomena
  • color categories/nameability -- certain colors may have associations with names, concepts

• Cartographic Communication (Kenneth E. Foote and Shannon Crum, The Geographer's Craft Project, Department of Geography, University of Colorado at Boulder)