On the left is a map of Mount Saint Helens
in geodetic coordinates produced from the National Elevation Dataset. The
map appears stretched in the east-west direction due to the smaller
physical distance between longitude points at this high latitude. On the
right is a UTM projection of the same NED data by 3DEM. The east-west
distortion has been removed, giving a map of the terrain that will match
the physical appearance of the surface.
Another example using a map of Tasmania
from the GTOPO30 DEMs is shown below. On the left is a map produced
from a GTOPO30 DEM in its original geodetic format. On the right is
a map from the same DEM resampled by 3DEM into a UTM projection.
There are some restrictions to this
conversion. Areas to be converted must be contained within a single UTM
zone. UTM zones are north-south strips of 6 degrees longitude in width
around the circumference of the globe. UTM conversions cannot be made for
areas that cross zone boundaries or that cross the equator. Areas to be
converted must also be contained between 84 degrees North latitude and 80
degrees South latitude.
Also note that conversion to UTM coordinates can be helpful in application
of terrain overlays. In the United States, most DRG and DOQ overlays are
available in UTM coordinates. Converting the terrain to UTM will
facilitate matching the terrain and overlay to one another.
