10 M DEM and Derivative Layers Posted!

Mike Brouillette, VCGI

VCGI is happy to announce the release of a new 10m statewide DEM and derivative layers from the recently completed (Jan. 2012) statewide 1/3 arc-second (~10m) DEM from the USGS National Elevation Dataset (NED). The NED is a multi-resolution dataset so for areas where LiDAR data exists the vertical accuracy is higher and subsequently the derived contours won’t match the 7.5′ USGS Quad Contours very well. See the Abstract section of ElevationContours_CN20T for more on this issue.

While the layer ElevationContours_CN20T can be custom downloaded, i.e. “clipped and zipped”, the other datasets are statewide in extent and compressed to “zip” files due to their size. These zip files contain both metadata and layer files you can elect to use in ArcGIS.

NEW LAYERS:

  • ElevationDEM_DEM10m               (342 Mb) – 10m DEM
  • ElevationContours_CN20T            (990 Mb) – 20′ contours
  • ElevationOther_ASPECT10m         (358 Mb) – Aspect identifies the down slope direction of the maximum rate of change in value from each cell to its neighbors. Values rounded to nearest Integer.
  • ElevationOther_HILSH10m            (299 Mb) – Hillshade from 315 degree azimuth and 45 degree altitude
  • ElevationSlope_SLOPE10m           (135 Mb) – Reclassed “percent rise” slope values rounded to nearest integer.

DATA ISSUES:

  • USGS states the NED can be used for hydrologic modeling but VCGI has not conducted any verification. It is highly recommending you review this issue before investing substantial resources in a modeling project.
  • WaterHydro_VHD – These features are based on the earlier black and white Orthophotos (1994-2000), and will not necessarily match up with the 10m DEM or the latest vintage of Orthophotos (2005-2010).
  • VTHYDRODEM – Created in 2004, this VT “hydrologically enforced” DEM (using the local resolution NHD for VT, i.e., the “VHD”) was interpolated from the VT Mapping Program orthophoto rectification X, Y, Z points to support the NHD effort and creation of “WaterHydro_VHDCARTO”, a cartographic version of the NHD with “intermittent” and “perennial” modeled streams. Having created it and working with ElevationDEM_DEM10m I would say the latter is more accurate. However, this raster does have the advantage of being integrated with the VHD.
  • ElevationContours_CN100T and *_CN50T – These are not currently based on the 1/3 arc-second NED and will be replaced sometime in 2012. Until then they will not be coincident with *_CN20T.

The following pre-existing contour data will be superseded by ElevationDEM_DEM10M

  •  ElevationContours_CN20T06A     20 ft contours from Ortho DEM – Addison, Wash, Orange Cnty
  •  ElevationContours_CN20T06B    20 ft contours from Ortho DEM – Rutland & Windsor Cnty
  •  ElevationContours_CN20T07      20 ft contours from Ortho DEM – Chit, Lam, Caledonia Cnty
  •  ElevationContours_CN20T08      20 ft contours from Ortho DEM – GrandIsl, Frank, Orlean Cnty
  •  ElevationContours_CN20T09      20 ft contours from Ortho DEM – Essex Cnty

Please feel free to contact me directly with questions, feedback about the metadata and any content or grammatical errors: Mike Brouillette, mailto:mikeb@vcgi.org

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