April 16, 2007

National Elevation Data (NED) added/modified since March 30, 2004

A memorandum of understanding (MOU) with the United States Geologic Survey (USGS) has allowed regular updates of the NED data that is the same as that held in http://seamless.usgs.gov/. The database is sent to NCGC as SDE/Oracle tables and extracted when you place your order.

As previously available in the Gateway, the dataset is provided in essentially two resolutions. The first is the 10 meter or better database that is 10 meters, 5 meters, 1/3 arc-second, 1/9 arc-second. The second is the 30 meter ~1 arc-second data that is updated over large areas by integrating 10 meter source data (where available) , re-sampled to ~1 arc-second.

The http://seamless.usgs.gov/ allows you to select 10 meter NED that is re-sampled from 30 meter. Available here is only true 10 meter NED or better.

There are some important changes from what was previously distributed.

• The maps are in GeoTIFF format instead of ESRI Grid
• The NED 10 maps are now 7.5 x 7.5 minute quadrangles instead of 30x60.
• The maps have pyramids generated and statistics calculated.
• There is no longer a need to distribute “nedshd10m _<nnnnnqd>” or “nedshd30m _<nnnnn>“shaded relief maps since they can be easily generated from the GeoTIFF with Spatial Analyst.
• There is no longer a need to distribute “nez30m _<nnnnn>“or “nezshd30m _<nnnnn>” maps for the one degree overlap at the UTM zone boundary because of “re-projecting on the fly”.
• There is no longer a need to distribute the “nedmeta10m_<nnnnnqd>“ shape files of 10 meter individual quadrangles that compose the 10 Meter NED because the 10 meter NED is a 7.5x7.5 minute quad with 10 meters, 5 meters, 1/3 arc-second, 1/9 arc-second resolution.
• The new map names are “ned10m<nnnnnqd>” and “ned30m<nnnnnqd>” instead of “ned10m_<nnnnnqd>” and “ned30m_<nnnnnqd>” to allow you to recognize the older version of NED maps.

There are a significant number of quads updated since the last update for both NED10 and NED30. Rather than present an extremely long list of quadrangles which have been updated, please refer to the status map which show the updates.

In addition, instead of looking for updates and ordering those, perhaps you would prefer to simply get a new copies of all your NED10 and NED30 maps because the older version that were ArcGrid format have been deprecated.