Maps and the electronic successors of maps, namely Geographic Information Systems (GIS), have been used for ages to describe the lay of the land. Planimetry on maps and area calculation in GIS are used to estimate extent of an area of interest, for example a stand of trees. If no map is available, a chain and compass (Fig. 2.1) or Global Navigation Satellite System (GNSS) receiver can be used to determine the boundary of an area of interest. Most modern GNSS receivers include a function to estimate the area described by a set of points (coordinates).

Chain distances and compass directions can be entered in a GIS or drawn on scale, which allow for areas to be estimated. Dimensions can be drawn on a scaled diagram and the area of the resulting polygon determined by subdividing it in a series of regular figures, for example triangles (Fig. 2.1 A, B, C). Calculating area from coordinates can be done via many methods. One such formula is provided below:

Area = 2 {(Y1X2 C Y2X3 ••• C YnXi) — (Xi Y2 C X2Y3 •

where

Xj is the x coordinate of vertex 1 Yn is the y coordinate of the nth vertex.

Area is a by-product of the mapping procedure (GIS) or from image processing, e. g., classification, and is discussed again in the section on Remote Sensing methods.