High Resolution 1:10,000 scale Mapping Strategy of Multi ... - NDMA

BASE MAP INFORMATION
Land surface reference information describes streams, roads, buildings, and
administrative boundaries that show the background context for mapping the flood
hazard zone.
The new methods typically use a digital orthophoto as the base map,
supplemented by planimetric vector data for key map features (e.g., roads needed
for georeferencing building locations) and administrative boundaries (e.g., city or
county boundaries) that cannot be observed in photography. An orthophoto is an
aerial photograph from which all relief displacement and camera tilt effects have
been removed such that the scale of the photograph is uniform and it can be
considered equivalent to a map. The elevation data input to floodplain mapping, has
a much greater effect on the accuracy of floodplain maps and base flood elevation
(BFE) is an important component of those maps.
BASE FLOOD ELEVATION (BFE)
Land surface elevation information defines the shape of the land surface,
which is important in defining the direction, velocity, and depth of flood flows. Land
surface elevation data for flood management studies of individual streams and rivers
have traditionally been derived by land surveying, but the very large aerial extent of
floodplain mapping, which covers the areas adjacent to streams and shorelines,
means that land surface elevation data for flood map modernization are mostly
derived from mapped sources, not from land surveying.
Land surface elevation information is combined with data from flood hydrology
and hydraulic simulation models, to define the BFE, which is the water surface
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