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The plot size and number of plots needed for a UFORE project are not fixed, although
UFORE plots are usually .1 acre in size (circle with 37.2 foot radius).
The number of plots needed depends on the accuracy needed. Typically 200 plots will
produce about a 10% standard error for the total number of trees. In the past,
smaller cities have used 30 plots and larger cities such as New York and Baltimore
have used approximately 200 plots.
A UFORE project typically begins with digital aerial photographs and land use maps of the
study area, which are usually available for individual cities from local agencies. If
these maps and photos are not locally available, the can be obtained from the
USGS for free or at low-cost. The
digital map is used in
selection of field plot locations; aerial photographs aid field crews in determining the
location of the plots. Where available,
digital versions of aerial photographs can greatly simplify and speed up the
sampling process. A
computer
program that randomly selects plots and locates them on aerial photographs is
available.
After field plots are located on aerial photographs, whether electronically or
manually, the plot locations are typically transferred to a street map of the area
for ease of navigation for field crews. Where field plots were located on digital,
geo-referenced photographs, plot locations can also be identified by their unique
latitude and longitude. This allows the use of the geographic positioning system
(GPS) units to locate the plots in the field.
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