Corners of LSASW bounding rectangles

The Large-scale Study Area Southwest (LSASW) focuses on the region drained by the Arkansas River and all but the lowest reaches of the Red River. To facilitate assembling a set of co-registered datasets describing land surface characteristics for the LSASW, a rectangular region has been defined which is centered on Kansas and Oklahoma, includes most of Colorado, New Mexico, Missouri, and Arkansas, covers southern Nebraska and northern Texas, and takes in smaller parts of Wyoming, Iowa, Illinois, Tennessee, Mississippi, and Louisiana.

To increase the usefulness of these datasets, they are being compiled in two different map projections which are widely used for the conterminous 48 United States, and also in geographic coordinates (longitude and latitude), although these latter give rise to grid cells which are neither square nor equal in area. The map projections supported are

To define the rectangular boxes, the maximum and minimum longitude and latitude needed to encompass the river basins were determined first, a buffer strip about one degree wide added, and the resulting values expanded outwards to the nearest integers. For each of the map projections, the minimum and maximum values of the x (easting) and y (northing) coordinates on the boundaries of the longitude/latitude box were determined, and expanded outwards to the nearest multiple of 10,000 meters for the Albers projection and to the nearest odd multiple of 500 meters for Lambert. The choice of an odd multiple of 500 meters was made to achieve registration with 1-km land cover and elevation datasets compiled by EROS Data Center.

The corners and dimensions of the boxes are as follows:

                                                          Dimensions 
                   Min X     Max X   Max Y    Min Y      E-W      N-S

  Long/Lat(deg)    -108.0    -90.0     41.0     32.0     18.0      9.0
        (arcsec)  -388800  -324000   147600   115200    64800    32400

  Lambert Azimuth -758500   946500  -393500 -1442500  1705000  1049000

  Albers         -1130000   570000  2070000   990000  1700000  1080000
The corners specified above should be used with GIS software packages such as Arc/Info. For gridded data used with image processing packages such as LAS or ERDAS, the coordinates of the upper left corner of the image specified by the LAS .ddr file or in the ERDAS header record refer to the center of the upper left pixel; i.e., they are offset by one-half pixel from the corner of the bounding rectangle (the necessary adjustments are made automatically by Arc routines such as IMAGEGRID and GRIDIMAGE). To overlay data at different resolutions, therefore, the LAS/ERDAS upper left corner easting or longitude should be increased by one-half the grid cell size, and the northing or latitude decreased by one-half the grid cell size.

Projection Parameters

Lambert Azimuthal Equal Area

This projection is suitable for maps covering the 48 conterminous U.S. states and is centered in South Dakota. It has been used by the EROS Data Center (EDC) for a series of land surface charactristics data sets.

	Projection units:	meters
	Spheroid:		sphere of radius 6,370,997 meters
	Central longitude:	-100 deg (W)
	Central latitude:	45 deg N
	False easting:		0
	False northing:		0

Albers Equal Area

This projection is also widely used for maps covering the conterminous 48 states, and is centered in southeast Kansas.

	Projection units:	meters
	Spheroid:		Clarke 1866
	1st standard parallel:  29 deg 30 min N
	2nd standard parallel:	45 deg 30 min N
	Central meridian:	-96 deg (W)
	Latitude of origin:	23 deg N
	False easting:		0
	False northing:		0

Last change: 4 Nov. 1997, R. A. White / raw@essc.psu.edu