ESRI Map Service for USA Topo

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05-09-2013 06:53 AM
MichaelLohr
Occasional Contributor II
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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CharlieFrye
Esri Contributor
The vertical datum varies by the source data.  The original contours for the U.S. were created using the National Elevation Dataset (NED), which uses the North American Vertical Datum of 1988.  For more details see the NED FAQ.

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CharlieFrye
Esri Contributor
The vertical datum varies by the source data.  The original contours for the U.S. were created using the National Elevation Dataset (NED), which uses the North American Vertical Datum of 1988.  For more details see the NED FAQ.
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MichaelLohr
Occasional Contributor II
Thanks for the reply, Charlie. The link to the NED FAQ spells out all the detail on the vertical datum, including that in the conterminous US, all elevations are NAVD88 Meters, but some areas outside may be other datums. I verified this by checking some old scanned hardcopies of a USGS quad map and comparing the online streamed version from the ESRI mapping service.

It matched up being NAVD88 Meters. Your reply led to the answer.

I would think someone would want to edit the description on ther USA Topo service to include a description of the vertical datum and a link to the NED info, like you provided.
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