Point, line, and polygon data that describe ideal USGS quadrangle boundaries and cornor points for quadrangles that intersect the state of Illinois. ISGS, 1992 (revised 1998). Includes line and polygon feature classes for each of the following scales/extents:

• 3.75-minute x 3.75-minute, commonly called quarter-quadrangles, typically used for a 1:12,000-scale index,
• 7.5-minute x 7.5-minute, the common USGS topographic sheet extent, typically 1:24,000-scale in Illinois,
• 15-minute x 15-minute, typically used for 1:62,500-scale index,
• 30-minute x 1 degree, typically used for 1:100,000-scale index,
• 1-degree x 2-degree, typically used for 1:250,000-scale index.