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Thematic Mapping

Thematic Mapping. Thematic Mapping. Objectives of map design Data measurement Basic statistical concepts and processes Thematic map representations. Objectives of map design. Geographical variables are so diverse and complex, we must understand their essential nature.

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Thematic Mapping

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  1. Thematic Mapping

  2. Thematic Mapping • Objectives of map design • Data measurement • Basic statistical concepts and processes • Thematic map representations Thematic Mapping

  3. Objectives of map design • Geographical variables are so diverse and complex, we must understand their essential nature. • Geographical ordering - locational relationships. • Discrete phenomena. • Continuous phenomena. Thematic Mapping

  4. Data measurement • Scales of measurement • Nominal • Ordinal • Interval • Ratio • Use of the scales of measurement in thematic mapping Thematic Mapping

  5. Nominal scales of measurement Examples of differentiation of point, line and area features on a nominal scale of measurement. After Robinson, et al., 1995 Thematic Mapping

  6. Major Minor Smoke pollution Ordinal scales of measurement Examples of differentiation of point, line and area features on an ordinal scale of measurement. After Robinson, et al., 1995 Thematic Mapping

  7. Interval-ratio scales of measurement Examples of differentiation of point, line and area features on an interval or ratio scale of measurement. After Robinson, et al., 1995 Thematic Mapping

  8. Basic statistical concepts and processes • It is often necessary to manipulate raw data prior to mapping. • Pre-map data manipulation stage: • Making data to be mapped comparable. Thematic Mapping

  9. Absolute and derived data • Absolute qualities or quantities: “raw data” maps showing landuse categories, production of goods, elevations above sea level, etc. • Derived values. • Summarisation or relationship between features. • Four classes of relationships: averages, ratios, densities and potentials. Thematic Mapping

  10. Averages • Measures of central tendency • Three commonly used averages in cartography: • Arithmetic mean • Median • Mode Thematic Mapping

  11. Arithmetic mean Arithmetic mean Geographical mean Thematic Mapping

  12. Median and mode • Median - the attribute value in the middle of all ordered attribute values • Geographic median - the attribute value below which and above which half the total area occurs • Mode - the value that occurs most frequently in a distribution • Area modal class - the class which occupies the greatest proportion of an area Thematic Mapping

  13. Ratios • Something per unit of something else • Quantities that are not comparable should never be made the basis for a ratio Thematic Mapping

  14. Densities • Relative geographical crowding or sparseness of discrete phenomena Thematic Mapping

  15. Potentials • Individuals comprising a distribution (e.g. people or prices) interact or influence one another. • The gravity concept: Thematic Mapping

  16. Thematic map representations • Indices of variation • Mode - variation ratio • Median - quantile range (quartiles, ceciles or centiles (percentiles)) • Arithmetic mean - standard deviation Thematic Mapping

  17. Scaling systems Thematic Mapping

  18. Some basic statistical relations • Regression analysis • Correlation analysis • Spatial autocorrelation Thematic Mapping

  19. Example Thematic Mapping (Source: Robinson, et al., 1995)

  20. Regression analysis Scattergrams with fitted linear regression line. Thematic Mapping

  21. Areal units Thematic Mapping

  22. Observed, predicted and residuals Maps showing observed per capita educational expenditures, predicted per capita educational expenditures based on per capita income, and residuals from the regression. From Robinson, et al., 1995 Thematic Mapping

  23. Observed, predicted and residuals (cont.) Maps showing observed numbers of first-degree graduates, predicted numbers of first-degree graduates based on per capita income, and residuals from the regression. From Robinson, et al., 1995 Thematic Mapping

  24. Classification • Natural breaks • Equal interval • Equal area • Quartile • Standard deviation Thematic Mapping

  25. Maximum = 30127 Minimum = 0 Mean = 291.3 Std = 1947.1 Example: world population density Thematic Mapping

  26. Natural breaks Class 1 Class 2 Thematic Mapping

  27. Natural breaks(cont.) Thematic Mapping

  28. Equal interval Class 1 Thematic Mapping

  29. Equal interval(cont.) Thematic Mapping

  30. Equal area Class 3 Class 4 Class 5 Class 1 Class 2 Thematic Mapping

  31. Equal area (cont.) Thematic Mapping

  32. Quartile Class 1 Class 2 Class 3 Class 4 Class 5 Thematic Mapping

  33. Quartile (cont.) Thematic Mapping

  34. Standard deviation 0 - 1 Std -1 Std - 0 Mean Mean = 291.3 SD = 1947.1 Thematic Mapping

  35. Mean +1 Std +2 Standard deviation Mean = 291.3 SD = 1947.1 Thematic Mapping

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