<P> In geology or geography, the word "quadrangle" usually refers to a United States Geological Survey (USGS) 7.5 - minute quadrangle map, which are usually named after a local physiographic feature . The shorthand "quad" is also used, especially with the name of the map; for example, "the Ranger Creek, Texas quad map". These maps are one - quarter of the older 15 - minute series . On a quadrangle map, the north and south limits of the quadrangle are not straight lines, but are actually curved to match Earth's lines of latitude on the standard projection . The east and west limits are usually not parallel as they match Earth's lines of longitude . In the United States, a 7.5 minute quadrangle map covers an area of 49 to 70 square miles (130 to 180 km). </P> <P> The surfaces of other planets have also been divided into quadrangles by the USGS . Martian quadrangles are also named after local features . </P>

Why is it called a 7.5 minute map