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A quadrangle is defined by north and south boundaries of constant 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]
In the United States, where the primary national series is organized by a strict 7.5-minute grid, they are often called or quads or quadrangles. Topographic maps conventionally show topography, or land contours, by means of contour lines. Contour lines are curves that connect contiguous points of the same altitude .
DOQs produced by the USGS cover an area measuring 7.5-minutes longitude by 7.5-minutes latitude (the same area covered by a USGS 1:24,000-scale topographic map, also known as a 7.5-minute quadrangle) or 3.75-minutes by 3.75-minutes.
The largest (both in terms of scale and quantity) and best-known topographic series is the 7.5-minute, 1:24,000 scale, quadrangle, a non-metric scale virtually unique to the United States. Each of these maps covers an area bounded by two lines of latitude and two lines of longitude spaced 7.5 minutes apart.
Booth, Derek B.; Troost, Kathy Goetz; Shimel, Scott A. (2008), Geologic Map of Northeastern Seattle (Part of the Seattle North 7.5 X 15-minute Quadrangle), King County, Washington: Geologic Summary, United States Geological Survey; Bretz, J Harlen (1913), Glaciation of the Puget Sound Region (PDF), Washington Geological Survey.
Map produced with DLG data. DLGs are normally derived from USGS maps or USGS map-related sources. DLGs are distributed at three different scales: large-scale, which normally correspond to the USGS 7.5- by 7.5-minute, 1:24,000 and 1:25,000-scale topographic quadrangle map series, 1:63,360-scale for Alaska and 1:30,000-scale for Puerto Rico; intermediate scale, which are derived from the USGS 30 ...
When such block-spanning occurs, data are shifted to start cleanly on each block boundary. A records also come in "old" and "new" flavors, because the USGS added several fields to the A record. One of the key items is the quadrangle, which is a set of four terrestrial coordinates describing the four-sided polygon enclosing the area of interest.
New Mexico Bureau of Mines and Mineral Resources Stratigraphic Chart Series. 1; Smith, G.A.; Kuhle, A.J. (1998). "Geology of the Santo Domingo Pueblo and Santo Domingo Pueblo SW 7.5-minute quadrangles, Sandoval County, New Mexico". New Mexico Bureau of Mines and Mineral Resources Open-File Map Series. OF-GM 15/26