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Map Basics

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

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  1. Map Basics GEOG 370 Christine Erlien, Instructor

  2. Map Basics • Maps as a language • Symbolization • Scale • Simplification/generalization • Grid systems • Projections

  3. Value of Maps • Way to record & store information • Way to analyze locational distributions & spatial patterns • Method of presenting information & communicating findings

  4. Value of Maps

  5. Graphicacy • Understanding graphic devices of communication • Maps • Charts • Diagrams • Why? • Understanding usage of graphic devices increases our abilities • Describing spatial phenomena • Making decisions

  6. Maps • Model of reality, not a miniature version • Media for delivering geographic information • Target audience determines level of abstraction, map scale, symbology

  7. 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

  8. 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:

  9. Cartographic abstraction & generalization • Selection • Classification • Simplification • Symbolization

  10. Selection • Decisions about • Area to be mapped • Map scale • Map projection • Data variables • Data gathering/sampling

  11. Classification • Organizes mapped information • Qualitative or quantitative • Qualitative: Spatial distribution of nominal or ordinal data • Quantitative: Spatial aspects of numerical data

  12. Classification of interval/ratio data • Dividing data into categories • Natural breaks • Quantile breaks • Equal intervals • Standard deviation

  13. 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

  14. 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

  15. Classification of interval/ratio data • Equal intervals • Range between lowest & highest values divided equally among the number of classes

  16. 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

  17. From Longley et al. Geographic Information Systems and Science

  18. Generalizing features From How To Lie with Maps, M. Monmonier

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

  20. 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

  21. 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?

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

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

  24. Dot distribution: nominal point symbols

  25. 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

  26. Thematic map types: Proportional dot http://goliath.frostburg.edu/rpotts0/ProportionalCircleMapB.jpg

  27. Thematic map types: Ordinal line http://clerk.ci.seattle.wa.us/~ordpics/115137At10TRFigA4.gif

  28. Thematic map types: Ordinal area

  29. 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

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

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

  32. Bertin’s visual variables Hue: Colors perceived Value: Lightness/darkness Saturation: Intensity/purity

  33. Major Map Elements • Necessary components of a typical map • Title • Legend: Interpretive key to symbols • Symbols: Used to describe features • Scale bar • North arrow

  34. Major Map Elements • Necessary components of a typical map • Projection • Cartographer • Date of production

  35. Map Elements • Some elements are used to selectively assist effective communication • Neatlines: Used to frame map • Inset maps: Close-up view • Charts • Additional text

  36. Map Elements Border Neat line Title Figure Legend Ground Scale Credits Inset Place name North Arrow

  37. 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

  38. 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

  39. Methods of illustrating map scale • Graphic scale • Measured ground distances appear on map • Change with changes in scale of output

  40. 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

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