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ESRI Map Service for USA Topo

Question asked by mll@johnsoneng.com on May 9, 2013
Latest reply on May 15, 2013 by mll@johnsoneng.com
We use this map service from the ESRI servers as an added layer in online maps. It is great and adds a lot of content from the USGS Quadrangle map series.

My question is what the vertical datum is for the contour elevation lines that are shown when zoomed in? Traditionally, these have been referenced to National Geodetic Vertical Datum (NGVD) of 1929. Since the map service is providing seamless scanned data from the USGS maps, I would assume that the online version has the same vertical datum reference. But nowhere in the map service details does it actually say what the vertical datum is, unless I missed it. It should be stated clearly as in a lot of areas, this older datum is no longer in use, and there can be significant differences between NGVD 29 and the newer datums, depending on your geographic location.

Thanks for any help.

http://services.arcgisonline.com/ArcGIS/rest/services/USA_Topo_Maps/MapServer

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