Since the process of hydrologic enforcement (in order to create a continuous surface water flow) may potentially mask out features in low-relief areas such as wetlands or sinkholes, the workgroup has discussed the option of providing two versions of DEMs (hydro enforced and non-hydroenforced). USGS would cost-share ($350 state share) on the DEM version that adheres to USGS standard policy of hydro-enforced "where appropriate". The costs for doing 2 versions (un-enforced, enforced) of the same DEM will cost the state $1050 ($350 + $700). USGS NMD encourages Kentucky personnel to help determine which DEMs would be appropriate for hydro enforcement.

USGS has estimated that most of the revisions will be needed in the Eastern and Western Kentucky coal mining areas having extensive surface mining activity. The Kentucky workgroup has pointed out that there are other areas that need to be considered for revision such as urban and industrial growth areas, highway projects, and some floodplain areas, where the topography might have changed due to recent floods. USGS has proposed to photo-inspect all quads and work with representatives from Kentucky to determine the exact revision needs.

The Kentucky workgroup has pointed out that there may be a need to retain the original elevation data captured from the topographic quadrangle in DEM format before any revisions are made. Those "un-revised" DEMs can possibly be delivered to OGI as an intermediate product, before doing the stereo-grammetric revisions. However, there may be additional costs associated with that proposal.

According to initial USGS estimates, about 190 quads would need revision. These quads are located mostly in Eastern and Western Kentucky coal mining areas. However, this number is subject to change as the topographic quads are photo-inspected.

The Kentucky workgroup has investigated an option to do a softcopy stereo-photogrammetric inspection and revision of the entire state, rather than use regular photo-inspection to determine the subsequent elevation revision needs.

USGS has estimated that the cost of such inspection alone would be approximately $1,000 per quad state share. That does not include any subsequent revision cost. If this option were used, subsequent revision costs could be reduced due to the costs associated with model setup would already be part of the inspection process.

Based on USGS experience with using local spatial data, there usually are edge matching problems when trying to merge local data with surrounding USGS elevation data. Those seams are inevitable due to the varying accuracy, resolution and production-process characteristics that exist in different source data sets. There are processes available to minimize those differences to some degree, but it is difficult to eliminate them completely.

There are also considerable difficulties that can surface when trying to integrate numerous data sets of various datums, coordinate systems, accuracy, resolution, and type (grid, contour, random points, etc) into a common data model. Each of these sources will have to be dealt with uniquely. USGS has had mixed results trying to make homogeneous datasets (especially in appearance) out of scattered and variable sources. Integrating elevation data from various sources, is a concept being developed for the USGS National Elevation Dataset (NED), but that concept needs extensive testing. Any previous experience of Kentucky expertise in merging elevation datasets will be valuable for USGS.

Also, the data rights and licensing issues need to be negotiated with the local agencies, since many local agencies charge for their data. However, the data integrated into the statewide dataset would probably be resampled to a lower resolution, and any reverse engineering of high resolution elevation data would be impossible.