NOTE that geographic coordinates are NOT a projection -- scales vary with latitude and are substantially different in the x and y directions, and the 30-arcsec grid cells are neither square nor equal in area.
The spheroid in terms of which the latitude and longitude are defined has the following characteristics:
Datum: NAD27 Spheroid: CLARKE1866 Units: arcsecondsRelative to this cooordinate system, the polygon version of the dataset has the following bounding coordinates:
Xmin = -449054 (124°44'14" W) Xmax = -241021 (66°57'01" W) Ymin = 88365 (24°32'45" N) Ymax = 177784 (49°23'04 N)For the 30-arcsec grid version, the bounding coordinates were extended outwards to an exact multiple of 1 arcminute, giving
Xmin = -449100 (124°45' W) Xmax = -241020 (66°57' W) Ymin = 88320 (24°32' N) Ymax = 177840 (49°24' N) nrow = 2984 ncol = 6936 cellsize = 30For most image processing software packages, the coordinates of the center of the upper left (northwest) cell should be entered as
x = -449085, y = 177825