What is Thematic Mapping

In contrast to general maps, these maps emphasize on geographic areas of a particular region for data analysis. These maps provide information or data related to the percentage unemployed, the population explosion, climate or soil type of a particular area. Thematic maps are also known as graphic essays that use 'base data' of places and coastlines as a reference point.

The use of thematic mapping can be traced in 1686, when Edmond Halley, an English astronomer published a map called the terrestrial map. He featured the map in his article about trade winds. This was the earliest meteorological chart that came into being. The use of thematic mapping became prominent in 1854, when John Snow, a physician from London, used thematic principles to devise a map to analyze spread of disease (cholera) in a particular area. His method of mapping included the use of Geographic Information System, which comprised locations of pumps and streets in the neighborhood of London. The outbreak of cholera was mapped, and the emerging pattern directed to a pump located on Broad Street. With the removal of the pump it was revealed that a sewer line was passing beside it.

Thematic maps provide location-specific information and can be compared with patterns of other maps. Maps consisting of demographic data of the density of population are good examples of thematic maps. In terms of designing a thematic map, spatial patterns and detailed visual perception along with the presentation should be taken into consideration. There are different types of thematic maps which represent the application of these maps.

Symbol Maps
Like the name suggests, these maps use symbols that vary in size to denote a particular region. The symbols used vary in accordance with the proportion of quantities represented by the symbol. A symbol adds to the effectiveness of a search in a map.

Choropleth Maps
This is a common example of a thematic map. Choropleth maps make visualization of a particular area in a region relatively easy. If you consider the population of a certain region, you can use color as a symbol for that region. Areas with less population can be shaded with a light color whereas densely populated areas can be shaded using darker colors.

Bivariate Maps
These maps explore the possibilities of using two variables on a map. It can be a combination of sets of colors or symbols. Determining the population density and rainfall in a particular region could be two variables on a map. You can denote symbols or colors for the two variables.

Dot Maps
As the name suggests the symbol used to denote an occurrence is a dot. The dots used should be uniform in appearance. For example, a cluster of dots can represent multiple entities. In case of multiple entities different colors are used.

Isopleth Maps
These maps simplify data with a process of continuous distribution. These maps are used for mapping atmospheric pressure and environmental data. Lines are used to connect points which represent a certain value.

Dasymetric Maps
Dasymetric maps depict quantitative volumetric data of a particular area. These maps are extensively used by cartographers for mapping population density. These types of maps use standardized data. The need for dasymetric maps became popular as they provided methods for accurate and detailed visualization for mapping population density.

Thematic maps act as an important reference tool, used for mapping frequent occurrences of geographical concepts such as density or climate in a particular region.