These data are in a Lambert Conformal Conic projection and coordinate units are feet. Tabular data for quadrangle polygon include quadrangle name and USGS map designation code. Each quad is annotated with its name. Tabular data for the arcs include latitude or longitude in decimal degrees. 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 have been added at every quadrangle corner. Vertices have been added to every arc at 1.5' intervals to reduce shape changes due to projection of the data. Arcs and polygon topology have been added for the Danby quad in southwestern Illinois, increasing the number of quadrangles to 1072. Two attribute values have been corrected.