In which type of map are areas shaded according to a prearranged key, representing ranges of values?

A choropleth map is a specific type of thematic map designed to visualize data across geographic areas by shading them according to a predefined key. This shading corresponds to ranges of values, allowing viewers to quickly understand spatial patterns and variations in the underlying data. For instance, in a choropleth map depicting population density, areas might be colored from light to dark based on how densely populated they are.

This style of mapping effectively communicates information by grouping data into categories and displaying it visually, making it easier to see trends and differences across regions at a glance. It offers a clear representation of quantitative data as it relates to geographical areas, highlighting how certain ranges of values can vary by location.

Thematic maps encompass a broad category of maps used to dedicate specific themes or topics beyond just geographic features, but the specificity of a choropleth map accurately describes the method of shading based on values. Other types of maps listed, like isarithmic and proportional symbol maps, represent data differently, focusing on continuous data or symbols whose sizes correspond to numeric values, respectively.