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Chorochromatic maps (from Greek for 'area' and 'color; also known as area-class or qualitative area maps) map nominal data using various colors, shades of black and white, or even patterns. In a chorochromatic map the data decides the boundaries. Colors are mapped according to data boundaries instead of trying to make locations fit within existing political boundaries. Only nominal data should be graphed, and there can be no indication of data hierarchy or order.  Soil maps and biome maps are common examples of chorochromatic maps.
Uses of Chorochromatic Maps
Chorochromatic maps can be simple or compound. In simple chorochromatic maps, single features with patchy occurrence are depicted (for example, to show the distribution of forest reserves or coal fields in a country). Compound chorochromatic maps on the other hand show phenomena in which types and categories can be recognized. Chorochromatic maps can be used to show different types of soil, rocks, vegetation, etc. For example, in a full vegetation map, all different kinds of vegetation are shown on the same map, using different symbols or shading patterns. Usually the classification resulting in the identification of the unit types shown on a compound chorochromatic map is qualitative, based on apparently discontinuous features. However, in certain cases (for example, soil and vegetation) the aggregate unit area characteristics form parts of a continuum. Cartographers should be aware that chorochromatic maps that display non-area-related phenomena like religion or language may cause the map reader to misinterpret the map. The map reader may assume that the size of the area is proportional to the number of people in the area with that qualitative characteristic. To avoid misleading the map user, the cartographer can add a diagram showing the actual numbers involved. 
Differences between Chorochromatic and Choropleth Maps
One of the main differences between chorochromatic maps and choropleth maps is in the way regions are formed. While the regions on choropleth maps are defined by preexisting borders (such as state boundaries), the regions on chorochromatic maps are defined by the data. For example, the display map, USDA Plant Hardiness Zone Map, shows that the regions change based on variations in plant hardiness zones, not preexisting political boundaries.
Another difference between chorochromatic and choropleth maps, is the use of quantitative data and nominal data. Chorochromatic uses nominal data. Choropleth maps most often use qualitative data. Because of this difference, choropleth maps use a color progression in order to show continuity, or a gradient of change. Since chorochromatic data is nominal, a color progression is not necessary to present data, because the fields or polygons are not related. Chorocromatic maps use one color per region.
The creation of regions, or polygons, is another difference between the two map types. Choropleth maps use pre-existing borders, or arbitrary borders, such as countries, states, etc. The regions in chorochromatic maps are created by the data. Borders change based on the values demonstrated by the geographic phenomenon.
- Kraak, Menno-Jan and Ferjan Ormeling, Cartography: Visualization of Geospatial Data, 2nd ed., Harlow, England: Prentic Hall, 2003,129.
- Adejuwon, O.(1975). "A Note on the Comparison of Chrochromatic Surfaces." Oxford, Blackwell Publishing. Geograhpical analysis: an internationl journal of theoretical geography Vol. 7, p-435-440. ISSN 0016-7363.
- Kraak, Menno-Jan and Ferjan Ormeling, Cartography: Visualization of Geospatial Data, 3rd ed., New York City: Rutledge, 2010,140.