This is an alphanumeric combination of degrees north and west with a row column index applied to each 1 degree by 1 degree area. TILE - Row and column index to quadrangles. Illinois DNR designation. Rows move north to south and columns west to east. Quad T0101 is USGS 42091-E1.
Values are in decimal degrees.
Q15 - Indicates if arc is also a boundary for a 15 minute quad. 0 - arc is not a 15 min. 0 - arc is not a 7.5 min. 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.