Background cartogram or choropleth (from Greek χώρο- + πλήθ [ος] , "place, region" + "value") is a type of cartogram on which the intensity of an indicator within the territorial unit is depicted by shading of various densities or paints of various degrees of saturation [1] .
Three types of background cartograms are known: simple, dasimetric, and unclassified. Variables are usually the value (in the HSV color model ) and texture. Background cartograms are among the most common cartograms for representing numerical values in a GIS [2] .
Content
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Simple
To create a simple background cartogram, an indicator value is set for each territorial unit and divided into categories or classes; choose the option of texture or paint for each category and fill it with each territorial unit. The number of categories is limited by the number of colors and textures that the eye can distinguish. To create simple background cartograms, only the values of the indicator and the boundaries of territorial units are needed [3] .
Dasimetric
Dasimetric [4] background cartograms are less common; they were developed to overcome some of the limitations of simple background cartograms [5] . As in simple background cartograms, in dasimetric ones, uniformly colored territorial units are used, as well as a breakdown of the indicator values into categories. In contrast to the simple version, in the dasimetric one determines the areas with similar values and the limits of the rapid change in the indicator values.
Dasimetric background cartograms have some simple limitations: it is impossible to establish the exact values of the indicator, and it is impossible to show smooth changes in the values of the indicator. However, since in the established territorial areas there is some uniformity of the indicator values, dasimetric background cartograms are closer to the real picture [5] .
Unclassified
Unclassified background cartograms were proposed by Waldo Tobler in 1973, but remained less common until the advent of the computer age. In non-classified background cartograms, each value of the indicator corresponds to a separate texture or paint [6] .
See also
- Heatmap
Notes
- ↑ A. T. Oprya. Statistics. - Kiev: Center for Academic Literature, 2012. - 448 p. with. - ISBN 978-611-01-0266-7 .
- ↑ Tyner, 2010 , p. 160.
- ↑ Tyner, 2010 , p. 161.
- ↑ The method of dasimetric cartography was developed by V.P. Semenov-Tian-Shansky
- ↑ 1 2 Tyner, 2010 , p. 163.
- ↑ Tyner, 2010 , p. 164.
Literature
- Judith A. Tyner. Symbolizing Volumes with Polygons: choroplethic maps // Principles of map design. - The Guilford Press, 2010 .-- 160-169 p. - ISBN 978-1-60623-544-7 .
- Michael P. Peterson (2008), "Choropleth Map", in Karen K. Kemp, Encyclopedia of Geographic Information Science , SAGE Publications, pp. 37–39, ISBN 978-1-4129-1313-3