Elevation on Blueprints
When a site plan is done without benefit of knowing how the grade of the site relates to sea level, an on-the-ground survey can still be performed, but the elevations represented by the survey will not relate to sea level. They will relate to an arbitrary and fictitious elevation established by the designer to show how one part of the site relates to another, and how the house or building relates to the site. Usually, the designer will pick a number easy to remember and work with...like 100... as the starting point.
So, if you plan shows the first floor of you house being at an elevation of 100, you can relate that "elevation" to the rest of your lot by reading the elevations provided on the plan to show you where the land is lower than your first floor, higher than your first floor, where it slopes gently or steeply, but all in relation to your first floor not sea level.
Is that sufficiently confusing?
[This message has been edited by treebeard (edited February 14, 2003).]