A map that uses graded differences in shading or color or the placing of symbols inside defined areas on the map in order to indicate the average values of some property or quantity in those areas WordNet 3.0 & Open English WordNet

A choropleth map is a type of statistical thematic map that uses pseudocolor, meaning color corresponding with an aggregate summary of a geographic characteristic within spatial enumeration units, such as population density or per-capita income. Wikipedia

a thematic map in which areas are shaded or patterned in proportion to the measurement of some statistical variable, using geographic boundaries Wikidata

A thematic map in which the distribution of some property is shown using different colours. Wiktionary