map basics geog 370 christine erlien, instructor

Page 1

Map Basics

GEOG 370

Christine Erlien, Instructor

Page 2

Map Basics Maps as a language

– Symbolization

– Scale

– Simplification/generalization

– Grid systems

– Projections

Page 3

Value of Maps

Way to record & store information

Way to analyze locational distributions & spatial patterns

Method of presenting information & communicating findings

Page 4

Value of Maps

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Page 5

Page 6

Graphicacy Understanding graphic devices of

communication– Maps– Charts– Diagrams

Why? – Understanding usage of graphic devices

increases our abilities• Describing spatial phenomena • Making decisions

Page 7

Maps Model of reality, not a miniature version

Media for delivering geographic information

Target audience determines level of abstraction, map scale, symbology

Page 8

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

Page 9

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:

Page 10

Selection

Classification

Simplification

Symbolization

Cartographic abstraction & generalization

Page 11

Selection Decisions about

– Area to be mapped

– Map scale

– Map projection

– Data variables

– Data gathering/sampling

Page 12

Classification

Organizes mapped information

Qualitative or quantitative– Qualitative: Spatial distribution of nominal

or ordinal data

– Quantitative: Spatial aspects of numerical data

Page 13

Classification of interval/ratio data

Dividing data into categories– Natural breaks

– Quantile breaks

– Equal intervals

– Standard deviation

Page 14

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

Page 15

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

Page 16

Classification of interval/ratio data

Equal intervals – Range between lowest & highest values

divided equally among the number of classes

Page 17

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

Page 18

From Longley et al. Geographic Information Systems and Science

Page 19

Generalizing features

From How To Lie with Maps, M. Monmonier

Page 20

Symbolization

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

Page 21

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

Page 22

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?

Page 23

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

Page 24

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

Page 25

Dot distribution: nominal point symbols

Page 26

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

Page 27

Thematic map types: Proportional dot

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

Page 28

Thematic map types: Ordinal line

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

Page 29

Thematic map types: Ordinal area

Page 30

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

Page 31

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

Page 32

Principles of map design

Visual variables

– Jacques Bertin, 1967

– System for representing information based on the visual properties & arrangement of graphic symbols

Page 33

Bertin’s visual variables

Hue: Colors perceived

Value: Lightness/darkness

Saturation: Intensity/purity

Page 34

Major Map Elements

Necessary components of a typical map– Title

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

– Scale bar

– North arrow

Page 35

Major Map Elements

Necessary components of a typical map– Projection

– Cartographer

– Date of production

Page 36

Map Elements Some elements are used to selectively assist

effective communication– Neatlines: Used to frame map

– Inset maps: Close-up view

– Charts

– Additional text

Page 37

Legend

Scale

Credits

North ArrowPlace nameInset

Ground

Figure

Neat lineBorder

Title

Map Elements

Page 38

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

Page 39

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

Page 40

Methods of illustrating map scale

Graphic scale– Measured ground distances appear on

map– Change with changes in scale of output

Page 41

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