NAD 83 is not related in any way to a specific vertical datum.

I am looking at Boston Inner Harbor Chart (NOAA 13272) which references NAD 83 and WGS 84.

The vertical datum on this chart happens to be "mean sea level".

However, I have a chart showing the "Relation of Datum Planes in Massachusetts" showing the relationship of U.S.C.&G.S. Mean Sea level to 43 other nearby vertical datum planes.

So, the answer is the vertical datum plane is independent of the spheroid "plan" approximation used by the mapping entity.

You will need to establish or assume a vertical datum plan for your project.

Thanks eriew, just as your response came in I got a follow up email from the County stating that the vertical datum used for their data is NAVD 88 (the same as our surveyor). Apparently the NAD 83 and NAVD 88 can be independent of each other so I imagine you could tie any vertical datum to the information.

Hello d_m_rosenberg:

I have copied this direct from WIKIPEDIA. hopw you find it useful.

babybear

North American Datum

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The North American Datum is the official datum used for the primary geodetic network in North America. In the fields of cartography and land-use there are currently two North American Datums in use: the North American Datum of 1927 (NAD 27) and the North American Datum of 1983 (NAD 83). Both are geodetic reference systems, but each is based on different measurements.

[edit] North American Datum of 1927

The North American Datum of 1927 (NAD27) is a datum based on the Clarke Ellipsoid of 1866. This Ellipsoid was created by way of manual surveying of the entire continent. The geodetic "center" of NAD-27 is a base station at Meades Ranch in Kansas.

[edit] North American Datum of 1983

As satellite and remote sensing technology both improved and were made available for civilian applications, it became obvious that the NAD-27's appromixations were not sufficiently accurate.

The North American Datum of 1983 was created to meet requirements for better accuracy and more precision. It is based on the GRS80 ellipsoid; an ellipsoid derived from satellite geodesy.

[edit] Comparisons Between NAD-27 and NAD-83

A point having a given latitude and longitude in NAD27 may be displaced on the order of many tens of meters from another point having the identical latitude and longitude in NAD83. So it is important to specify the datum along with the coordinates. The North American Datum of 1927 is defined by the latitude and longitude of an initial point (Meades Ranch in Kansas), the direction of a line between this point and a specified second point, and two dimensions that define the spheroid. The North American Datum of 1983 is based on a newer defined spheroid (GRS80); it is an Earth-centered datum having no initial point or initial direction.