What type of thematic map uses graduated colors or shading patterns to represent statistical data for predefined areas?

Question

Accepted Answer

Choropleth map. A choropleth map uses colors, shading patterns, or tinting applied to predefined geographic areas (such as countries, states, counties, or census tracts) to represent the intensity or magnitude of a statistical variable within each area. Examples include maps showing population density by county, median household income by state, or election results by district. The visual variation in color intensity allows viewers to quickly identify spatial patterns and regional differences in the mapped variable.

An isoline map (or isarithmic map) uses lines that connect points of equal value across a continuous surface, such as isotherms (equal temperature), isobars (equal pressure), or contour lines (equal elevation). This type of map is designed for continuous phenomena rather than data aggregated within predefined boundaries. A dot distribution map uses dots placed within geographic areas to show the presence, quantity, and distribution of a phenomenon, where each dot represents a specified number of occurrences. This approach shows distribution within areas rather than applying uniform shading to entire regions. A proportional symbol map uses symbols (usually circles) of varying sizes placed at specific locations to represent the magnitude of a variable at that point, which shows data at point locations rather than shading entire areas.

Thematic map types are important cartographic knowledge tested on the DSST exam. Students should be able to identify different types of thematic maps and understand which type is most appropriate for different kinds of data. Choropleth maps are among the most commonly encountered thematic maps but have limitations, including the tendency to obscure variation within areas and the visual bias created by the size of geographic units (the modifiable areal unit problem).

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