Accuracy: How accurately must the position be
recorded? While it is possible to obtain accuracies of
less than 1 centimeter, there are not many uses on
farms that require that level of accuracy, especially
considering that the equipment costs upwards of
$40,000. Since the Department of Defense turned
Selective Availability (the intentional degrading of the
GPS signal accuracy) off, accuracies of less than 10
meters can be obtained with low-cost recreational GPS
receivers, and receivers with WAAS DGPS capabilities
can often provide accuracies of less than 5 meters.
The ability to determine locations within 15 feet is
adequate for many basic mapping applications on
farms. For example, the exact location associated with
a soil sample is meaningless since each bog or box of
soil sent to the lab is a composite of several samples
representing a fairly large area. Therefore, a GPS
receiver with 10 meter or better accuracy is suitable for
recording the locations of soil samples.