Equalarea

Equal-area, or equal-area projection, is a class of map projections that preserves the size of geographic regions when mapping the globe to a plane. In an equal-area projection, the area of any region on the map is proportional to its true area on Earth, allowing direct visual comparison of territory sizes. This makes equal-area projections useful for thematic and statistical maps where data are tied to area, such as land use, resource distribution, or population density by region. Distortion in equal-area projections occurs in shape, distance, and angles, and the pattern of distortion varies by projection. No equal-area projection preserves all geometric properties simultaneously.

Common examples include the Lambert cylindrical equal-area projection, the Mollweide projection, and Goode’s homolosine projection, as well as the Albers equal-area conic and the Lambert azimuthal equal-area projection. Cylindrical equal-area projections preserve areas across latitudes but distort polar regions; Mollweide and Goode’s homolosine offer more balanced distortion for world maps. Albers equal-area conic is often preferred for fields spanning mid-latitudes, while azimuthal forms are used for focused polar or hemispheric views.

Applications and limitations: equal-area projections are favored for comparative analysis of geographic data, choropleth maps, and any visualization where area represents quantity. They are less suitable when accurate shapes or local angles are important, and distortions can be pronounced away from standard lines or poles in many projections.

See also: cartography, map projection, conformal projection, equal-distance projection.