Topographic surveys depict the terrain (vertical character) of the land by showing contour lines on the survey map that are labeled with the elevation. A contour line follows the lay of the land at the labeled elevation.
Topographic surveys are prepared with reference to, or relative to a particular Vertical Datum. In some zoning jurisdictions no specific datum is required if the property is not near a water body or in a flood zone. If a specific datum is required, it will usually be the North American Vertical Datum of 1988 (NAVD88) which is the current datum in use on FEMA Flood Insurance Rate Maps and is required for a FEMA Elevation Certificate.
The NY State Department of Environmental Conservation (DEC) also requires the National Geodetic Vertical Datum of 1929 (NGVD29) 10 foot contour line to be shown on a proposed site plan as a criteria for determining the status of the DEC jurisdiction over a proposed waterfront site improvement project.