The semi-major axis of the ellipsoid used is 6378206.4 meters. This is an alphanumeric combination of degrees north and west with a row column index applied to each 1 degree by 1 degree area. Values are in decimal degrees. Q100 - Indicates if arc is also a boundary for a 30' x 60' quad. This data set was created to serve as base map information.
Data are appropriate for use at a regional scale and are intended as a reference.
Data are not appropriate as a geodetic or engineering base. Tics were generated as well, one at each quad corner. Latitude and longitude values were assigned to the arcs in the generation process. The data were projected to Lambert Conformal Conic. Arcs forming quadrangle boundaries for any 15 minute quadrangles intersecting Illinois were extracted to this data set.