shrug-l: RE: Elevation Unit Reference for NAVD88

Tripp Corbin tcorbin at
Tue Jul 10 09:36:41 EDT 2012

The North American Vertical Datum of 1988 (NAVD 88) is the vertical control
datum established in 1991 by the minimum-constraint adjustment of the
Canadian-Mexican-U.S. leveling observations. It held fixed the height of the
primary tidal bench mark, referenced to the new International Great Lakes
Datum of 1985 local mean sea level height value, at Father Point/Rimouski,
Quebec, Canada. Additional tidal bench mark elevations were not used due to
the demonstrated variations in sea surface topography, i.e., the fact that
mean sea level is not the same equipotential surface at all tidal bench


Tripp Corbin, MCP, CFM, GISP | Chief Executive Officer
 <> eGIS Associates, Inc.

tcorbin at | 

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From: shrug-l-bounces at
[mailto:shrug-l-bounces at] On Behalf Of Sykes, John
Sent: Tuesday, July 10, 2012 9:25 AM
To: Thomas, Jim; shrug-l at
Subject: shrug-l: RE: Elevation Unit Reference for NAVD88




NAVD88 is a datum.  Elevations in NAVD88 relate to the NAD83 ellipsoid and
has little relationship to local sea level.  Therefore, "xx.xx ft (NAVD88)"
would be the proper citation.


I believe that elevations relating to local sea level would be listed as
"xx.xx ft( AMSL)"  which would refer to a local benchmark that has been
surveyed to the local sea level.  NOAA costal charts list the various sea
level datums for a specific location, and the survey data is referenced to
it.  I might be wrong on the second point, it has been several years since I
had to work with sea level data.


Again, someone feel free to jump in on this, it has been a long time since I
worked with sea level data (1999 in the Florida Keys).


-- John 



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From: shrug-l-bounces at
[mailto:shrug-l-bounces at] On Behalf Of Thomas, Jim
Sent: Tuesday, July 10, 2012 8:50 AM
To: shrug-l at
Subject: shrug-l: Elevation Unit Reference for NAVD88


I all,


I have a survey question related to elevation units.  Since NAVD88 ZERO and
MSL Zero are not necessarily the same, is it wrong to express elevation
units that reference NAVD88 as 'FT AMSL'?  Or is 'ft' more appropriate?


I've seen data stored this way and I would like to suggest the appropriate





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