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Cartographic abstraction

Cartographic abstraction. Summary session GEO381/550 October 5 th , 2004. Outlines. Basics Geographic phenomenon Describing data distribution Components of cartographic abstraction Data classification Quantitative classification methods Simplification Map symbolization

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Cartographic abstraction

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  1. Cartographic abstraction Summary session GEO381/550 October 5th, 2004

  2. Outlines • Basics • Geographic phenomenon • Describing data distribution • Components of cartographic abstraction • Data classification • Quantitative classification methods • Simplification • Map symbolization • Visual variables by measurement scale • Map types by the behavior of geographic phenomenon

  3. Basics Geographic phenomenon Measurement scale Data distribution

  4. Geographic phenomenon • Location, Scale • Spatial dimension • Continuous vs. discrete • Q. number, Mars, human organ • Q. Tornado path, elevation • Q. Temperature, cold/hot, population, population density

  5. Measurement scale of geographic phenomenon Year, land use, elevation, strongly agree/strongly disagree, religion, coffee consumption, national income, occupation

  6. Describing data distribution

  7. Histogram and descriptive statistics

  8. Components of cartographic abstraction Selection Classification Simplification Symbolization

  9. Selection preliminary steps • Classification • Simplification data processing • Symbolization choosing symbols

  10. Classification • Group values into class such that geographic pattern can be better revealed

  11. How do you determine class boundary? • Equal interval • put any number of values into class with the same interval • Quantile • put the same number of values into class • Natural break • marginal change in values • Standard deviation • how much deviated from the mean?

  12. Data classification method Equal interval Quantile l1 l2 l3 l4 l5 a1 a2 a5 a4 a5 σ  Natural break Standard deviation

  13. Simplification • Alter geometry such that relevant details are pronounced while irrelevant details are suppressed Line simplification Area dissolution

  14. Criteria for symbolization • Measurement scale  visual variables • Use ordering visual var. for quantitative scale • Use distinguishing visual var. for qualitative scale • The behavior of phenomenon  map types • Observed in a discrete/continuous scale & in a abrupt/smooth frequency • Maps sometimes reflect the way data collected rather than phenomenon. (e.g. crime is reported in the unit of jurisdiction)

  15. Appropriate use of visual variables- measurement scale -

  16. Appropriate choice of map types - behavior of phenomenon - Because of the discrepancy between phenomenon and data, we need to process data by manipulating spatial scale…. Handling GIS data well is an essential skill for advanced map-making!

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