Agriculture Reference
In-Depth Information
hoW Spot eLevationS are uSed By
contractorS
Construction contractors rely on spot elevations in establishing and
guiding most if not all their work. Typically, a contractor will set up
land-surveying equipment at the construction site, then set up a system
of stakes marked with desired spot elevations to guide earth moving
or setting the forms for hardscape and other work. The contractor may
also lay out a grid in areas where the grading plans contain contours,
then establish subgrade and finish grade spot elevations at each grid
intersection to guide construction. In the eyes of most contractors, spot
elevations have priority over contours. This does not mean that contours
are not utilized. Contours do establish the design intent of the designer;
however, they may be converted through interpolation into a grid of spot
elevations, or they may establish key elevations to guide construction of
the project.
hoW to caLcuLate a Spot eLevation
The same formula used to calculate the percent of slope of a ground or
paved surface is also used to calculate spot elevations: S = V / H (see Fig-
ure 10.16). To use this formula in making a spot elevation calculation, a
reference elevation is needed. A reference elevation is simply a known
elevation on a project site such as a bench mark, existing building floor
elevation, road centerline elevation, or any other existing physical fea-
ture, including property line corners or elevation information contained
in a surveyor's topographic survey.
The best way to learn how to calculate a spot elevation is to start
out with an example. In Figure 10.17 the elevation (spot elevation) of
point A is 32.5. It is located at the entrance to a building. Let's say that
we want to determine the elevation for point B in the figure.
