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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 Summary session GEO381/550 October 5th, 2004
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
Basics Geographic phenomenon Measurement scale Data distribution
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
Measurement scale of geographic phenomenon Year, land use, elevation, strongly agree/strongly disagree, religion, coffee consumption, national income, occupation
Components of cartographic abstraction Selection Classification Simplification Symbolization
Selection preliminary steps • Classification • Simplification data processing • Symbolization choosing symbols
Classification • Group values into class such that geographic pattern can be better revealed
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?
Data classification method Equal interval Quantile l1 l2 l3 l4 l5 a1 a2 a5 a4 a5 σ Natural break Standard deviation
Simplification • Alter geometry such that relevant details are pronounced while irrelevant details are suppressed Line simplification Area dissolution
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)
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!