What type of data might a thematic map illustrate?

A thematic map is designed to focus on a specific theme or subject area, presenting data that is related to that theme across geographic regions. In this case, demographics such as population density represent a social or economic theme that can be effectively illustrated using a thematic map. This type of map visually showcases how population density varies in different areas, allowing for the identification of trends, patterns, and relationships in population distribution.

While the other options may represent useful information, they do not align with the primary purpose of a thematic map. Topographical features generally involve physical geography and might be more suited to relief maps, while weather patterns are usually represented in met maps. Geological formations also pertain to earth science and are represented in geological maps. Each of these options focuses on different aspects of geography or science rather than the demographic data central to the definition of a thematic map.