Sector Sampling—Synthesis and Applications

Sector sampling is a new and simple approach to sampling objects or borders. This approach would be especially useful for sampling objects in small discrete areas or “polygons” with lots of internal or external edge, but it may be extended to sampling any object regardless of polygon size. Sector plots are wedge-shaped with a fixed sector angle. The probability of object selection is constant and equal to the sector angle in degrees divided by 360°. A unique property of sector sampling is that the point from which the angle originates may be located subjectively when the sector direction is at random. Another advantage over traditional sampling (such as fixed or variable area plots) is that there is no edge effect; that is, there is no altering of selection probabilities of objects close to polygon boundaries. Various approaches are described for deriving polygon means and totals with their associated variances. We review the genesis of sector sampling and develop two new components: sub-sampling using fixed area plots and line sampling using the sector arcs as transects. Sector sampling may be extended to measuring a variety of objects such as trees, shrubs, plants, birds, animal trails and polygon borders.