2 Objectives of map design Data measurement Basic statistical concepts and processes Thematic map representations
Thematic Mapping3 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 Mapping4 Data measurement Scales of measurement Nominal Ordinal Interval Ratio Use of the scales of measurement in thematic mapping
Thematic Mapping5 Nominal scales of measurement PointLineArea TownRiverSwamp MineRoadDesert ChurchGraticuleForest Bench mark Boundary Census regions Examples of differentiation of point, line and area features on a nominal scale of measurement. After Robinson, et al., 1995
Thematic Mapping6 Ordinal scales of measurement Examples of differentiation of point, line and area features on an ordinal scale of measurement. After Robinson, et al., 1995 PointLine (roads)Area Large Medium Small National Provincial County Township Industrial regions MajorMinor Smoke pollution
Thematic Mapping7 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 PointLine (roads)Area
Thematic Mapping8 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 Mapping9 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 Mapping10 Averages Measures of central tendency Three commonly used averages in cartography: Arithmetic mean Median Mode
Thematic Mapping11 Arithmetic mean Geographical mean
Thematic Mapping12 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 Mapping13 Ratios Something per unit of something else Quantities that are not comparable should never be made the basis for a ratio Ratio or rateProportionPercentage
Thematic Mapping14 Densities Relative geographical crowding or sparseness of discrete phenomena
Thematic Mapping15 Potentials Individuals comprising a distribution (e.g. people or prices) interact or influence one another. The gravity concept:
Thematic Mapping16 Thematic map representations Indices of variation Mode - variation ratio Median - quantile range (quartiles, ceciles or centiles (percentiles)) Arithmetic mean - standard deviation
Thematic Mapping22 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 Mapping23 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 Mapping24 Classification Natural breaks Equal interval Equal area Quartile Standard deviation