General FAQs Contour and Elevation Frequenly Asked Questions (FAQs)

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  • ?1) Who do I contact for more information?

    This data is intended primarily for internal NCDOT use. For questions concerning this data, please contact the GIS Unit; see the Contact Us information. For questions concerning specific software products, please contact your software vendor.​

  • ?2) Where can I find the most recent and most accurate LiDAR data?

    The most recent and accurate LiDAR data can be found at the North Carolina Floodplain Mapping Program web site: www.ncfloodmaps.com.​

  • ?3) Why is NCDOT providing this data when it is already available on the Floodplain Mapping web site?

    This web page is intended primarily for internal NCDOT use, but may be accessed by others. The Floodplain Mapping web site does not provide contours or countywide grids. Please consult the Floodplain Mapping web site to get the most current and accurate information.​

  • ?4) What is the difference between the May 2007 release and the older March 2005 data release?

    All of the data for this release has been generated from LiDAR sources and organization of the files has been altered.​

  • ?5) What is the accuracy of the LiDAR data on this web site?

    The vertical datum used is NAVD 88. The accuracy of the LiDAR is about 25cm or about 10 inches.

    Contours were generated directly from the 20-foot LiDAR DEM. These DEM grids already represent the hydrography breaklines that are included with the Floodplain Mapping data. ArcMap Geoprocessing was used to produce the contours but some of the very short contours were removed. ArcMap Geoprocessing produces engineering-quality contours, representing an exact interpretation of the lattice surface model. Cartographic quality contours, while more aesthetically pleasing, are based on a more subjective interpretation of the surface. We do not provide cartographic contours but some simple automated processing was done to improve the appearance. County governments may define more breaklines or have a more accurate DEM grid.
     
    Elevation was rounded to the nearest foot in order to reduce the file size. More precise Z values may be obtained from the Floodplain Mapping web site.
     
    Sometimes LiDAR has trouble in open water areas and the interpolation creates triangular areas that are incorrect. This may be most noticeable when viewing the hillside shading.

  • ?6) Where can other Elevation Data be found for North Carolina:

  • ?7) Where can other GIS Layers be found for North Carolina:

  • ?8) Which mountain area counties are too large to distribute as 2-foot contours?

    Alleghany, Ashe, Avery, Buncombe, Burke, Caldwell, Clay, Cherokee, Graham, Haywood, Jackson, Macon, Madison, McDowell, Polk, Rutherford, Swain, Transylvania, Wilkes, and Yancey.

    These counties will have 4-foot contours instead of the 2-foot. All of the contours are interpolated from the LiDAR 20-foot cells.

  • ?9) Why are some 2 foot contours missing?

    For a complete set of 2 foot contours, AutoCAD users should merge the 2 foot, 4 foot, 20 foot, and 100 foot contour files. Additionally, the origin should be set to 0,0,0.​
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