GIS Data Catalog

Summary

Comparable in purpose and use to the USGS Digital Elevation Model (DEM) data but generally of a higher level of accuracy and sample density.

Useful for a range of analytical and cartographic projects including flood hazard evaluation, geologic mapping, hydrologic modeling, slope and aspect determination, and line-of-sight calculations.

These data was processed through an extensive series of quality control steps by both the vendors and clients; however, they are still considered an interpretation or model of the earth's surface rather than an absolute point-to-point measure.

Further, the data are not without error due to incomplete editing, absence of sufficient point density, and other 'blunder' or erroneous points.

Finally, due to changing ground and vegetative conditions the quality and accuracy of the data vary considerably with areas of steep relief and/or dense vegetation exhibiting poorer quality than open flat areas.

This is due to a large variance in the number of points from area to area that are considered 'to-ground' values combined with the variance in absolute horizontal and positional accuracy of given points.

Users must make careful review of the fitness of these data for their particular use.

For many purposes a site- and use-specific field survey will be necessary.

In particular, derivation of contours, whether from the raw ascii points or a derived surface (i.e., lattice or tin), should be approached with caution due to the high variability of the data.

Contours generated at an interval finer than 5-feet may not meet necessary accuracy requirements for specific environmental or building purposes needs and do not take the place of a first-order ground survey.

Description

Last-return LiDAR data edited to remove 90-95% of vegetated and man-made elevated features.

Depicts - within limits of operational accuracy, point density and editing efficiencies - a 'bare-earth' interpretation of the earth's Also called Digital Ground Model (DGM), Virtually-Deforested (VDF) Model, or 'Mowed' Data is stored as ArcInfo Lattice Grids.