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A "quadrangle" is atopographic map produced by theUnited States Geological Survey (USGS) covering theUnited States. The maps are usually named after localphysiographic features. The shorthand "quad" is also used, especially with the name of the map; for example, "the Ranger Creek, Texas quad". A quadrangle is defined by north and south boundaries ofconstant latitude (which are not great circles so are curved), and by east and west boundaries of constant longitude.
From approximately 1947–1992, the USGS produced the 7.5 minute series, with each map covering an area one-quarter of the older 15-minute quad series, which it replaced.[1] A 7.5 minute quadrangle map covers an area of 49 to 70 square miles (130 to 180 km2).[2] Both map series were produced viaphotogrammetric analysis ofaerial photography usingstereoplotters supplemented by field surveys. These maps employ the 1927North American Datum (NAD27); conversion or a change in settings is necessary when using aGPS which by default employ theWGS84geodetic datum. Beginning in 2009, the USGS made available digital versions of 7.5 minute quadrangle maps based onGIS data that use theNAD83 datum, which is typically within one meter of WGS84, or within the uncertainty of most GPS coordinate measurements. The USGS also producesquarter quadrangle (QQ) maps of areas 3.75 minutes square.[3][4][5]
The surfaces of other planets have also been divided into quadrangles by the USGS.Martian quadrangles are also named after local features.[6]