======================================================================
=                       Quadrangle_(geography)                       =
======================================================================

                             Introduction                             
======================================================================
A quadrangle (or quad) is a region of the Earth's surface bounded by
two parallels (circles of constant latitude) and two meridians (lines
of constant longitude). The term is especially associated with
topographic maps produced by the United States Geological Survey
(USGS) of quadrangles covering the United States. Quadrangle maps are
usually named after local physiographic features; for example, "the
Ranger Creek, Texas quad".

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. A 7.5 minute quadrangle map covers an area
of 49 to. Both map series were produced via photogrammetric analysis
of aerial photography using stereoplotters supplemented by field
surveys. These maps employ the 1927 North American Datum (NAD27);
conversion or a change in settings is necessary when using a GPS which
by default employ the WGS84 geodetic datum. Beginning in 2009, the
USGS made available digital versions of 7.5 minute quadrangle maps
based on GIS data that use the NAD83 datum, which is typically within
one meter of WGS84, or within the uncertainty of most GPS coordinate
measurements. The USGS also produces quarter quadrangle (QQ) maps of
areas 3.75 minutes square.

The surfaces of other planets have also been divided into quadrangles
by the USGS. Martian quadrangles are also named after local features.


                               See also                               
======================================================================
* GEOREF quadrangle
* List of quadrangles on Mercury
* List of quadrangles on Venus
* List of quadrangles on the Moon
* List of quadrangles on Mars
* List of quadrangles on Io
* List of quadrangles on Ganymede
* List of quadrangles on Callisto
* Quadrilateral


 License 
=========
All content on Gopherpedia comes from Wikipedia, and is licensed under CC-BY-SA
License URL: http://creativecommons.org/licenses/by-sa/3.0/
Original Article: http://en.wikipedia.org/wiki/Quadrangle_(geography)


.