The directories which correspond to 7.5-minute quadrangles have four basic types of files.

.cor files are complete lists of Global Positioning System point files. These are cropped to extend 1/2 minute over edge where points exist in the over edge area. Horizontal coordinates are UTM NAD 83, meters. Vertical coordinates are meters. (These files are the best for doing coordinate transformations. They are formatted to read directly into NOAAs CORPSCON program)

.asc files are the same as .cor but reformatted to process into ARC/INFO coverage format. A customized ARC/INFO aml script file is recommended to process these files to an ARC/INFO coverage. The aml's are available upon request, contact vcaruso@usgs.gov.

.e00 files are ARC/INFO coverage format of the .asc files (use import in ARC to read them into ARC). Coordinate transformations are easily preformed in the ARC environment using these files. Topogrid is the recommended program for converting to lattice. *NOTE: For those wishing to create their own DEM'S, latticedem has a format error in the DEM record A field. Use the .dem files as described below instead of ARC generated DEM'S.

.dem and .dem.ths (tenths of feet - reflects highest resolution) are the DEMs which are under development and subject to change as we are able to edit, edge join, water body edit. Check these files per latest date for the most current version. We expect to have a "reasonably" finished DEM for all the quads by August 1. I will be replacing all the DEMs this week with DEMs cropped to 7.5-minutes and the grid resolution is now 30 meters UTM horizontal, NAD83 and tenths of feet vertical, NAVD 88. The extension is .dem.ths After that date we will be going back in to do some additional work adding break lines to better represent levies, roads, ditches (use demlattice in ARC)

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