Mathematically generated grid representing USGS 7 1/2 Minute Quadrangle Map outlines. Quadrangle names and standard identifiers are included with the data set.

USGS 1:100,000 scale Quadrangle Map Index derived from the larger scale double precision 7 1/2 Minute Quadrangle Index.

USGS 1:250,000 scale Quadrangle Map Index with quadrangle name and standard identifiers.