# Map coloring

Map coloring is the act of assigning different colors to different features on a map. There are two very different uses of this term. The first is in cartography, choosing the colors to be used when producing a map. The second is in mathematics, where the problem is to determine the minimum number of colors needed to color a map so that no two adjacent features have the same color.

## Cartography

A map of the United States using colors to show political divisions using the Four color theorem.
The US Presidential Election of 2004, visualised using a choropleth map
Topographic map of Easter Island, using colors to show elevations.

Color is a very useful attribute to depict different features on a map.[1] Typical uses of color include displaying different political divisions, different elevations, or different kinds of roads. A choropleth map is a thematic map in which areas are colored differently to show the measurement of a statistical variable being displayed on the map. The choropleth map provides an easy way to visualize how a measurement varies across a geographic area or it shows the level of variability within a region.

Displaying the data in different hues can greatly affect the understanding or feel of the map.[2] Also, the cartographer must take into account that many people have impaired color vision, and use colors that are easily distinguishable by these readers.[3]

Colors can also be used to produce three-dimensional effects from two-dimensional maps, either by explicit color-coding of the two images intended for different eyes, or by using the characteristics of the human visual system to make the map look three-dimensional.[4]

## Mathematics

In mathematics there is a very strong link between map coloring and graph coloring, since every map showing different areas has a corresponding graph. By far the most famous result in this area is the four color theorem, which states that any planar map can be colored with at most four colors.

## References

1. ^ Matt Rosenberg. "Map Colors - The Role of Colors on Maps".
2. ^ Robinson, A.H. (1967). "Psychological aspects of color in cartography". International Yearbook of Cartography 7. pp. 50––61.
3. ^ Brewer, C. (1996). "Guidelines for selecting colors for diverging schemes on maps". The Cartographic Journal 33 (2) (Maney Publishing). pp. 79––86.
4. ^ Eyton, J.R. (1990). "Color stereoscopic effect cartography". Cartographica: The International Journal for Geographic Information and Geovisualization (UT Press) 27 (1): 20–29. doi:10.3138/K213-2288-7672-U72T.