Thematic map

A thematic map is a type of map specifically designed to show a particular theme connected with a specific geographic area.

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. The contrast between them lies in the fact that thematic maps use the base data, such as coastlines, boundaries and places, only as points of reference for the phenomenon being mapped. General maps portray the base data, such as landforms, lines of transportation, settlements, and political boundaries, for their own sake.

Thematic maps emphasize spatial variation of one or a small number of geographic distributions. These distributions may be physical phenomena such as climate or human characteristics such as population density and health issues. Barbara Petchenik described the difference as "in place, about space." While general reference maps show where something is in space, thematic maps tell a story about that place (e.g., city map).

Thematic maps are sometimes referred to as graphic essays that portray spatial variations and interrelationships of geographical distributions. Location, of course, is important to provide a reference base of where selected phenomena are occurring.

An important cartographic element preceding thematic mapping was the development of accurate base maps. Improvements in accuracy proceeded at a gradual pace, and even until the mid-17th century, general maps were usually of poor quality. Still, base maps around this time were good enough to display appropriate information, allowing for the first thematic maps to come into being.

One of the earliest thematic maps was a map entitled Designatio orbis christiani (1607) by Jodocus Hondius showing the dispersion of major religions, using map symbols in the French edition of his Atlas Minor (1607). This was soon followed by a thematic globe (in the form of a six-gore map) showing the same subject, using Hondius' symbols, by Franciscus Haraeus, entitled: Novus typus orbis ipsus globus, ex Analemmate Ptolomaei diductus (1614)

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