Measuring the influence of individual vertices on polygon area: implications for errors in area estimates

S. Prisley and D. Daversa

Department of Forestry, Virginia Tech

It is quite common for GIS-derived estimates of forest stand area to be used in operational forest management activities such as timber harvesting, site preparation, and planting. To the extent that errors exist in the polygon area estimates, payments based on area may be incorrect, prescriptions may be misapplied, and projections of costs or revenues may be invalid. Using the formulae for polygon area as a function of vertex coordinates, it is possible to determine which vertices in a polygon boundary exert the most influence on polygon area. It happens that the best measure of influence of a polygon vertex is half the distance between its neighbors. Thus, adding unnecessary vertices to a polygon boundary will reduce the influence of individual vertices, but also may increase opportunities for error. This paper will present the conceptual and mathematical basis for measuring vertex influence, and then present results based on simulation and a test of field obtained, GPS-based area estimates.

Keywords: Accuracy, simulation, GPS

(presentation)