A thematic map is a type of map

Map

A map is a visual representation of an area—a symbolic depiction highlighting relationships between elements of that space such as objects, regions, and themes....

 or chart

Chart

A chart is a graphical representation of data, in which "the data is represented by symbols, such as bars in a bar chart, lines in a line chart, or slices in a pie chart"...

 especially designed to show a particular theme connected with a specific geographic area. These maps "can portray physical, social, political, cultural, economic, sociological, agricultural, or any other aspects of a city, state, region,nation , or continent".
A thematic map is a map that focuses on a specific theme or subject area, whereas in a general map the variety of phenomena—geological, geographical, political—regularly appear together.