There are three broad categories of maps. The first, reference maps, generally show several types of spatial data without specific emphasis on one type over another. Reference maps can vary in their complexity and size, but generally include just the various geographic features that give a picture of the area being mapped, e.g. political boundaries, cities, topographic features and/or transportation routes. For instance, in the reference map of Thailand below, major cities, roads, railways, rivers and country borders are shown and differentiated by symbol and label, but the map is not made explicitly for navigation or exploration of those features.
A second type of map is the thematic map, which as its name suggests, means the map has a specific theme or focus. This group of maps is extremely diverse. Thematic maps can vary in topic, complexity, purpose and kind of representation. They generally show characteristics, or attributes, of features that vary spatially. The attribute can vary in a qualitative or nominal way, e.g. categories of land cover; or the attribute can vary in a quantitative way, e.g. amount of precipitation. Thematic maps can represent data with points, lines, areas or volumes. Using visual variables (e.g. hue, lightness, pattern, shape) that fit logically with both the kind of feature being used for the symbols (e.g. point, line, area) and the way the attribute varies (qualitatively or quantitatively) is key to representing data in thematic maps. We will discuss symbolization in more depth in Lesson Two.
Special-purpose maps are a third category of maps. They lie somewhat between reference maps and thematic maps as they are often reference-like in their use but are made for specific types of users or pertain to a specific type of data. Navigational maps, like those in road atlases or nautical/aeronautic charts, are considered special-purpose maps, as are maps for certain industries or occupations, like Sanborn maps, soil maps, and municipal utility maps.
If you are interested in investigating this subject further, I recommend the following:
- Brewer, C. A. (2008). Designed Maps: A Sourcebook for GIS Users. Redlands, CA: Esri Press