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Map Basics. GEOG 370 Christine Erlien, Instructor. Map Basics. Maps as a language Symbolization Scale Simplification/generalization Grid systems Projections. Value of Maps. Way to record & store information Way to analyze locational distributions & spatial patterns

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map basics

Map Basics

GEOG 370

Christine Erlien, Instructor

map basics1
Map Basics
  • Maps as a language
    • Symbolization
    • Scale
    • Simplification/generalization
    • Grid systems
    • Projections
value of maps
Value of Maps
  • Way to record & store information
  • Way to analyze locational distributions & spatial patterns
  • Method of presenting information & communicating findings
  • Understanding graphic devices of communication
    • Maps
    • Charts
    • Diagrams
  • Why?
    • Understanding usage of graphic devices increases our abilities
      • Describing spatial phenomena
      • Making decisions
  • Model of reality, not a miniature version
  • Media for delivering geographic information
  • Target audience determines level of abstraction, map scale, symbology
maps as models a paradigm shift in cartography
Maps as Models: A paradigm shift in cartography
  • Communication paradigm -> analytical paradigm
  • Communication paradigm
    • Traditional approach to mapping
    • Map itself was a final product
      • Communication tool
    • Limits access to original (raw) data
maps as models a paradigm shift in cartography1
Maps as Models: A paradigm shift in cartography
  • Analytical paradigm
    • Maintains raw data in computer
    • Display is based on user’s needs
    • Transition ~ early ’60s
    • Advantage:
cartographic abstraction generalization
Cartographic abstraction & generalization
  • Selection
  • Classification
  • Simplification
  • Symbolization
  • Decisions about
    • Area to be mapped
    • Map scale
    • Map projection
    • Data variables
    • Data gathering/sampling
  • Organizes mapped information
  • Qualitative or quantitative
    • Qualitative: Spatial distribution of nominal or ordinal data
    • Quantitative: Spatial aspects of numerical data
classification of interval ratio data
Classification of interval/ratio data
  • Dividing data into categories
    • Natural breaks
    • Quantile breaks
    • Equal intervals
    • Standard deviation
classification of interval ratio data1
Classification of interval/ratio data
  • Natural breaks
    • Imposed
      • Fractions/multiples of mean income levels
      • Rainfall thresholds that support different vegetation types (e.g., arid, temperate)
    • Calculated by software
classification of interval ratio data2
Classification of interval/ratio data
  • Quantile breaks
    • Predetermined number of classes
    • Equal # observations in each class
    • 5 classes: good for uniform distributions
    • Limitation: Potentially misleading
      • Numeric size of each class rigid 
        • Numerically similar values may be in different classes
        • Wide-ranging values may be in same class
classification of interval ratio data3
Classification of interval/ratio data
  • Equal intervals
    • Range between lowest & highest values divided equally among the number of classes
classification of interval ratio data4
Classification of interval/ratio data
  • Standard deviation
    • Distance of observation from mean
    • GIS calculates mean value & generates class breaks in s.d. measures above & below
    • Using 2-color ramp helps emphasize values
generalizing features
Generalizing features

From How To Lie with Maps, M. Monmonier



map types
Map Types
  • Reference maps
    • Require conformity to standards
    • Examples: USGS topographic maps, navigation charts
  • Thematic maps
    • Cartographer has control over map design
    • Ex: Spatial distribution of variable
thematic map types dot distribution
Thematic map types: Dot distribution
  • Dot distribution
    • Dots, other small point symbols
    • Dot will represent a set number of a particular feature
    • If nominal symbols are used, will not vary in size. Why?

thematic map types p rop symbol
Thematic Map Types: Prop. symbol
  • Proportional Symbol
    • Graduated point, ordinal line symbol
      • Size of symbol proportional to size of data value
    • For areas  color, pattern
thematic map types proportional dot
Thematic map types: Proportional dot

thematic map types ordinal line
Thematic map types: Ordinal line

thematic map types choropleth
Thematic Map Types: Choropleth
  • Choropleth
    • Subdivisions are preexisting units
      • Example: Census tracts; county, state, national boundaries
    • Average value for areal unit is calculated & symbolized
    • Generally ratio values
      • Example: Population density, yield/acre, average income

principles of map design
Principles of map design
  • Visual variables
    • Jacques Bertin, 1967
    • System for representing information based on the visual properties & arrangement of graphic symbols

Bertin’s visual variables

Hue: Colors perceived

Value: Lightness/darkness

Saturation: Intensity/purity

major map elements
Major Map Elements
  • Necessary components of a typical map
    • Title
    • Legend: Interpretive key to symbols
      • Symbols: Used to describe features
    • Scale bar
    • North arrow
major map elements1
Major Map Elements
  • Necessary components of a typical map
    • Projection
    • Cartographer
    • Date of production
map elements
Map Elements
  • Some elements are used to selectively assist effective communication
    • Neatlines: Used to frame map
    • Inset maps: Close-up view
    • Charts
    • Additional text
map elements1
Map Elements


Neat line








Place name

North Arrow

map scale
Map Scale
  • Map scale: Ratio between map distance & ground distance
    • large scale map vs. small scale map
      • 1:250,000 > 1:1,000,000
      • Large scale map  more details
  • Scale-dependent map display in GIS
    • Minimum vs. Maximum map scale
methods of illustrating map scale
Methods of illustrating map scale
  • Verbal scale
    • Example: 1 inch equals 63,360 inches
    • Easily understood
  • Representative fraction scale
    • Example: 1:250,000
    • No units necessary  map & ground distance in same units as fraction
methods of illustrating map scale1
Methods of illustrating map scale
  • Graphic scale
    • Measured ground distances appear on map
    • Change with changes in scale of output
map scale vs scale generally
Map scale vs. scale generally
  • Large scale study vs. small scale study
    • Large scale study
      • Extensive in scope or scale
    • Small scale study
      • Small area or limited scope
    • In which study scenario will data be collected in more detail?
    • In the sense it is being used here  opposite the meaning of scale in map scale