Types of Thematic Maps
A cartogram is a map in which some thematic mapping variable – such as travel time, population, or GNP – is substituted for land area or distance. The geometry or space of the map is distorted, sometimes extremely, in order to convey the information of this alternate variable.
A choropleth map (from Greek χῶρος ("area/region") + πλῆθος ("multitude")) is a thematic map in which areas are shaded or patterned in proportion to the measurement of the statistical variable being displayed on the map, such as population density or per-capita income.
A thematic map is a map that focuses on a specific theme or subject area. This is in contrast to general reference maps, which regularly show the variety of phenomena—geological, geographical, political—together.
An Isarithmic map is a type of Thematic map that represents a continuous field using line and/or region symbols to connect places of similar value. It is sometimes called a heat map, although the term heat map should only be used for one type of isarithmic map that represents density.
It can be argued, thus, that proportional symbol maps “let the thematic data speak for itself,” since the size of the symbols relates directly to the thematic data and not just the footprint of the enumeration unit.