Corners of SRB bounding rectangle

The Susquehanna River Basin covers most of central Pennsylavania, part of west-central New York, and a small part of Maryland at the head of the Chesapeake Bay. To facilitate assembling a set of co-registered datasets containing land surface characteristics and model outputs for the SRB, a rectangular box has been defined which encloses the entire SRB, with boundaries extended outwards to an exact multiple of 10 km in the Albers projection used for Pennsylvania.

The boundaries and dimensions of the box are as follows:

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

  Albers Equal      -80000   290000   450000   60000    370000   390000
   Area Projection     (easting)         (northing)

  Approximate        -79.0    -74.5     43.0    39.5       4.5      3.5
    Lat/Long           (longitude)        (latitude)

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 should be increased by one-half the grid cell size, and the northing decreased by one-half the grid cell size. For the lower right corner, the easting should be decreased by one-half the grid-cell size and the northing increased by the same amount. For the pixel (grid) dimensions commonly used for SRB data sets, this yields the pixel-center coordinates at the upper left and lower right corners and the image dimensions which are given below.

Pixel Size     Image U. L. C.      Image L. R. C.         Image Size
 (meters)    Northing  Easting   Northing  Easting  (lines x pixels/line)

  10000       445000   -75000      65000   285000          39 x 37

   1000       449500   -79500      60500   289500         390 x 370

    100       449950   -79950      60050   289950        3900 x 3700

Projection Parameters

Albers Equal Area Conic

This projection, which is centered on Pennsylvania, has been used extensively for a number of datasets covering all or part of the state.

	Projection units:	meters
	Spheroid:		Clarke 1866
	1st standard parallel:  40.0° N
	2nd standard parallel:	42.0° N
	Central meridian:	-78.0° (W)
	Latitude of origin:	39° N
	False easting:		0
	False northing:		0

Note on Datum/Spheroid Conversion:

The standard Pennsylvania Albers projection is defined in terms of the Clarke 1866 spheroid, used with the NAD27 datum. Increasingly, new data sets are being referenced to the WGS84 spheroid and NAD83 datum derived from satellite geodesy. Within the region of the SRB, the coordinates of a point in the Albers projection defined in terms of NAD83 are greater than the coordinates for NAD27 by 22 to 26 meters in easting and 11 to 16 meters in northing.

Last change: 1998 May 22, R. A. White /