What is a Quadrangle?

The definition of a quadrangle varies, depending on the context. In geometry, a quadrangle — or, more commonly, a quadrilateral — is a figure with four sides and four corners. In architecture, the term is used for a courtyard that is surrounded on all sides by a building. One of the most common uses of the term is to refer to a quadrangle or "quad" map, a type of map produced by the United States Geological Survey (USGS). In these maps, all areas are divided into rectangles of 7.5 minutes, a measure of longitude and latitude.

On a quad map, quadrangles appear rectangular, but do not actually have parallel sides. On flat maps, the quadrangle can appear in the shape of a rectangle, but on globes and globe maps, the lines vary based on the curvature of the Earth. The left and right sides of the quadrangle feature lines running up and down, or north and south; the lines are not parallel, but stay along the universally recognized longitudinal lines. The east and west running lines on run along latitude lines and remain parallel to each other, but are not the same length. As a result, they meet the longitudinal lines at different points.

Each quadrangle on the USGS map ranges in area from 49 miles (78.8 km) to 70 miles (112.6 km). These squares are basic subdivisions of the Public Land Survey System by the USGS, which is used to identify land parcels around the country. Each quadrangle on the map can be divided further into 16 different townships and generally ranges to about 24 miles (38.6 km) on each side.

In a quad map, the quadrangle is most often named after a local land feature, such as a creek, crater, fault line, or plateau. For example, one quadrangle in Texas is known as the "Ranger Creek, Texas quad." It is named for the Ranger Creek, which is housed within its borders, and is known by that name on maps and in references.

These quadrangles, or topographic quadrangle maps, have not been limited to the Earth. They have also been established as geologic maps on other planets. The quadrangles on Mars, like the ones in the United States and other places of the world, have been named for local landmarks and identifying features.