choroplethkartor

Choropleth maps are a type of thematic map that uses colors or patterns to represent the value of a variable across predefined geographic areas. In Swedish usage, the term choroplethkartor refers to this type of map. The color intensity corresponds to the magnitude of the statistic for each area.

They rely on aggregated data mapped to spatial units such as municipalities, counties, or census tracts. Because raw data at individual level are not shown, choropleths emphasize spatial patterns of distribution rather than individual measurements. Normalization per capita or per area is common to enable fair comparisons.

Classification and color: Values are mapped to a color scale. Common classification methods include equal intervals, quantiles, and natural breaks (Jenks). Color palettes should be perceptually uniform; sequential palettes for single-signed values; diverging palettes for values around a meaningful midpoint. Legends should explain units and breaks.

Design considerations: The choice of geographic units and the modifiable areal unit problem means results can vary with boundaries. The color scheme should avoid misinterpretation due to small areas or boundaries; consider adding labels or interactive features. Use data suppression when values are suppressible.

Applications: Widely used in demography, economics, public health, election analysis, and environmental studies to show regional variation, trends, and disparities. They are especially effective for communicating regional patterns to a broad audience.

Variants and extensions: Bivariate choropleth maps encode two variables using two color channels; choropleth maps can be combined with additional layers in GIS or web maps. In digital formats, interactivity allows hovering to reveal values and normalization details.