Also called Plate Carrée and Simple Cylindrical, Equirectangular is composed of equally spaced, parallel meridians and latitude lines that cross at right angles on a rectangular map. Each rectangle formed by the grid is equal in area, shape, and size.
All meridians are straight lines.
All parallels are straight lines.
Equally spaced parallel meridians and latitude lines cross at right angles.
The scale is correct along all meridians and along the standard parallels (Environmental Systems Research Institute, 1992).
City maps, or other small areas with map scales small enough to reduce the obvious distortion.
Simple portrayals of the world or regions with minimal geographic data, such as index maps (Environmental Systems Research Institute, 1992).
Equirectangular is not conformal nor equal-area, but it does contain less distortion than the Mercator in polar regions. Scale is true on all meridians and on the central parallel. Directions due north, south, east, and west are true, but all other directions are distorted. The Equator is the standard parallel, true to scale and free of distortion. However, this projection may be centered anywhere.
This projection is valuable for its ease in computer plotting. It is useful for mapping small areas, such as city maps, because of its simplicity. The USGS uses Equirectangular for index maps of the conterminous US with insets of Alaska, Hawaii, and various islands. However, neither scale nor projection is marked to avoid implying that the maps are suitable for normal geographic information.
Source: Snyder and Voxland, 1989