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Elevation Data Sources

Overview | Raster/Grid Sources | Vector Contour Lines | NC LIDAR Elevation Data



Overview

Elevation GIS and CAD data comes in many forms, formats, and from many sources. The most accurate and useful elevation data for locations in North Carolina are LIDAR-based products discussed in the seperate section below.

If you are just looking to add shaded relief as a basemap layer, see shadedrelief.com or search for relief data.



Raster/Grid Sources

US NED data

A valuable online (publically available) source of raster-based or grid elevation data for locations outside of North Carolina is the USGS National Map. It has the following elevation data products available at US and International extents:

  • National Elevation Dataset (NED) - Regularly updated composite of the latest Digital Elevation Model (DEM) data for the US, and represents the most current and highest resolution DEM data available that USGS has produced. The entire United States has DEM coverage at 30 meter resolution (1 arc second, originally produced from topographic maps), and much of the country is available at 10 meter resoultion (1/3 arc second). For an expanded discussion,
    see the Libraries' DEM website.

  • DEM portal
  • DEM Discovery Portal - Search by location for DEMs.

    • Click the ArcIMS Map Interface link
    • Zoom to your location
    • Under "Layers" make the layer you are interested in active by clicking the round radio button next to a layer name you want to query/select (go by the colors)
    • Use the "i" button to click the title of a DEM data source, and view the layer details in the table below

    Layer details include source, cell size, datums, formats, coverage types, and download links.

  • Global Digital Elevation Model (GDEM) - 99% global coverage, 30 meter resolution.

  • Shuttle Radar Topography Mission (SRTM) - 80% global coverage, 30 and 90 meter resolution.

  • ETOPO1 - 1 arc-minute (approx. 2 km) global relief model of the Earth, includes land topography and ocean bathymetry. Also two versions - an "ice surface" version has the Greenland and Antartic ice sheets, and a "Bedrock" version has the underlying terrain.

  • GTOPO30 - Global Digital Elevation Model with a horizontal grid spacing of 30 arc seconds (approximately 1 kilometer).

The USGS also provides Web Map Service (WMS) links for Elevation data.

For NCSU affiliates, there are many elevation data sources including worldwide SRTM, GTOPO, and NED, on the Geodata Server, mostly from the ESRI Data and Maps collection. Click Here to execute a search for available data with the keyword "elevation."



Vector Contour Lines

Vector contour line data is often useful for visual or analytical purposes. Many local governments provide these data at varying contour intervals, for download from their websites. Click here for North Carolina local government GIS websites. Check both the "Lib Web" and "Dwnld" links. In many cases, vector contour data is already on the Geodata Server. For example, to download contour data for a large area within the City of Raleigh from their tiled interface would take much longer than downloading this single geodatabase.

An alternative option for locations in North Carolina is to use NC DOT's contour data, discussed near the bottom of this webpage. For locations outside of NC, either search Google for locally maintained data, or contact Data Services to discuss your need.



LIDAR Based Elevation Data for North Carolina

Following Hurricane Floyd's flooding damage, North Carolina embarked on a joint effort with FEMA to re-map the state's flood zones. A by-product of this work is detailed elevation data collected by airborne LIDAR sensors. (NOTE: Raw pre-processed LIDAR data can be obtained from the USGS CLICK website for research needs.)

For more information about the NC Floodplain Mapping Program (NCFMP), and full documentation on the LIDAR data collection process, go to http://www.ncfloodmaps.com.

A LIDAR workshop was hosted by NCSU on August 4, 2004, and it's website has presentations and links to LIDAR data activity in NC that were relevant at that time.

NC LIDAR data as viewed on the seamless.usgs.gov website

NC LIDAR data as viewed on the seamless.usgs.gov website. NED 1 arc second (30m) data is being shown for surrounding states.

Elevation data derived from LIDAR are available for North Carolina from the following sources:

NC Sparta Server
The NC Sparta Server is NCFMP's website for disseminating NC LiDAR data. The site is also accessed by going to http://www.ncfloodmaps.com, click "Digital Flood Maps" and then the "Download Data" tab.

From the download window, you may download by county data listed below. (Some data for some counties are not available for various reasons). If you only need a small portion of a county, you may want to only download the necessary files. To determine the file names of what you'll need, you must download the ELEVGRID shapefile by clicking the "Terrain Data Grids" link.

Download Tip: To download many files in one batch process, such as may be needed for getting a lot of the LIDAR data zip files for example, try a Firefox extension such as DownloadThemAll!.

  • Bare Earth - Each zip file contains a text file with X,Y,Z fields and a shapefile of surface water features used to force the DEM elevation values. In ArcMap, use the "Add XY Data" tool to import the points.

  • DEM 20 and DEM 50 - Each zip file contains an .asc file (ASCII text file). These .asc files contain coordinates and elevation values for twenty and fifty-foot spaced points, which may be converted to a raster based Digital Elevation Model (DEM). The 50ft DEM's elevation values have been hydro-corrected.

    To create a DEM from this file with ArcMap, use the "ASCII to Raster" conversion tool. It is recommended to specify the "Output data type" as Float, in order to preserve the elevation decimal values, especially for eastern NC locations.

Note: The coordinate system for these downloads is NC Stateplane, NAD 83, feet, and elevation values are in feet.


County 20' DEMs
NCSU Alumnus Tom Colson has compiled the above referenced LIDAR data into 20' resolution DEMs, tiled by NC county. The difference between these files and what NCDOT has available (see the next listing below) is that the elevation values in this collection have NOT been rounded to the nearest foot. Instead, the floating point elevation values have been retained, which can be especially significant for applications down east.

As of November 2007, this is an incomplete collection. The graphic below shows which counties are available. In addition to the counties shown below in the graphic, the following counties are available: Alexander, Alleghany, Caswell, Columbus, Davie, Graham, Robeson, and Stokes.

The files may be downloaded from http://geodata.lib.ncsu.edu/dem/nc_20f (publically accessible). There is a zip file for each county, which contains an .asc file, .prj file, and .xml metadata file. The .asc file must be converted to a raster using the "ASCII to Raster" conversion tool with the "Float" option.

Usage Tip from Tom: The floating point grids will require much more computer "horsepower" than the integer grids from DOT, discussed below. A work-around is to apply a constant of perhaps 10,000 to the floating-point values, and thus keep the attribute (elevation) precision.

NC DEMs by county, Tom Colson collection

  

  

  

  

  

  

  

  

NC Dept. of Transportation, GIS Unit
You may download 20' resolution DEMs by NC county from NC DOT, GIS Unit . This is the same data as available from the NC Floodmaps.com discussed above, already compiled into raster DEMs, but elevation values have been rounded to the nearest foot.

Also available from their website are Hillside Shade grids, Slope grids, and Contour vector data. FAQ's and further documentation are there too.


USGS National Map
NC LIDAR data has been incorporated into the National Elevation Dataset (NED) accessible through the USGS National Map for download.


NOAA Coastal Service Center, Digital Coast
LIDAR data is available for download for the Outer Banks and most of the US coastline from the NOAA Digital Coast website. These data were collected seperately than the statewide collection following Hurricane Floyd, and on multiple dates since the mid-90's through the present.


NCSU Campus Elevation Data
See the NCSU Campus GIS Data webpage for LIDAR data derivatives.



Go the the Libraries GIS Data List