Choropleth map

A thematic map that shades or colors geographic areas according to values associated with them. Its area-based encoding makes spatial patterns visible while aggregating data to defined boundaries.

Data classification: The process of grouping quantitative values into classes for display or analysis. Class breaks determine which areas share a shade and how differences appear.
Thematic map: A map designed to show the spatial distribution of a selected subject or variable. Choropleths are one way to map a theme across geographic space.
Proportional symbol map: A thematic map that scales symbols in proportion to values at geographic locations. Symbols can show totals without making large geographic areas dominate visually.
Population density: The number of people living within a unit of geographic area. It is a normalized measure often mapped to compare how densely areas are inhabited.
Areal interpolation: The estimation of values for new geographic zones from data measured in different zones. Reusing data across changed boundaries can alter mapped estimates and comparisons.
Color scheme: A planned set of colors arranged to communicate distinctions or ordered values. Sequential and diverging palettes signal different kinds of variation across mapped areas.
Spatial data: Data that describe locations, geographic features, or relationships in space. Mapped values must be linked to geographic areas or boundaries.
Cartogram: A map that distorts geographic area to represent a variable such as population or value. Cartograms give visual weight to the mapped quantity rather than land area.
Election map: A map showing geographic patterns in election results or political representation. Choropleths commonly shade districts by vote share, though area can distort impressions.
Spatial autocorrelation: The degree to which nearby locations have similar or dissimilar values. Neighboring shaded areas may form patterns that require spatial analysis to assess.

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