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

Method of presenting information & communicating findings

Value of Maps

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Graphicacy Understanding graphic devices of

communication– Maps– Charts– Diagrams

Why? – Understanding usage of graphic devices

increases our abilities• Describing spatial phenomena • Making decisions

Maps 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

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 cartography

Analytical paradigm– Maintains raw data in computer

– Display is based on user’s needs

– Transition ~ early ’60s

– Advantage:

Selection

Classification

Simplification

Symbolization

Cartographic abstraction & generalization

Selection Decisions about

– Area to be mapped

– Map scale

– Map projection

– Data variables

– Data gathering/sampling

Classification

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

Dividing data into categories– Natural breaks

– Quantile breaks

– Equal intervals

– Standard deviation

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 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 data

Classification of interval/ratio data

Equal intervals – Range between lowest & highest values

divided equally among the number of classes

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

From Longley et al. Geographic Information Systems and Science

Generalizing features

From How To Lie with Maps, M. Monmonier

Symbolization

http://www.colorado.edu/geography/gcraft/notes/cartocom/cartocom_f.html

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

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?

http://www.unl.edu/nac/conservation/atlas/Map_Html/Demographics/National/Minority_Operated_Farms/1997.htm

http://www.cdc.gov/hiv/graphics/images/dotmaps/83aids.htm

Dot distribution: nominal point symbols

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

http://goliath.frostburg.edu/rpotts0/ProportionalCircleMapB.jpg

Thematic map types: Ordinal line

http://clerk.ci.seattle.wa.us/~ordpics/115137At10TRFigA4.gif

Thematic map types: Ordinal area

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

http://personal.uncc.edu/lagaro/cwg/color/Choropleth-5Good.gif

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

Necessary components of a typical map– Title

– Legend: Interpretive key to symbols • Symbols: Used to describe features

– Scale bar

– North arrow

Major Map Elements

Necessary components of a typical map– Projection

– Cartographer

– Date of production

Map Elements Some elements are used to selectively assist

effective communication– Neatlines: Used to frame map

– Inset maps: Close-up view

– Charts

– Additional text

Legend

Scale

Credits

North ArrowPlace nameInset

Ground

Figure

Neat lineBorder

Title

Map Elements

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

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 scale

Graphic scale– Measured ground distances appear on

map– Change with changes in scale of output

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