yielded by a given piece of timber by measuring its diameter Hemispherical photography – estimates solar radiation and characterize plant canopy structure/density using photographs taken looking upward through an extreme wide-angle lens Surveying techniques Traversing – method of surveying used to establish sampling plots along a line or path of travel Chain – equivalent to 66 feet, widely used distance in surveying practices in the United States and other countries influenced by imperial Great Britain Line plot survey – plots taken at a regular predetermined distance along the traverse path Tools Pacing – quick method used to survey in the field, requiring calibration of one's "paces" (pair of footsteps) to a known distance (often a chain) Hand compass – a compact magnetic compass with a sighting device used to determine the location of plots for a given bearing Wedge prism – optical instrument typically made of glass ground at slight angles to refract light passing through it from the smaller width side of the prism to the thicker width side of the prism, calibrated to a desired plot size (basal area factor) Angle gauge – similar in principle to a wedge prism, although it must be held a fixed distance from the eye GPS – global satellite navigation systems used to determine the position of oneself and plots GIS – an information system capable of integrating, storing, analyzing, and displaying forest geographic information collected in the field Timber volume determination Site index – a species specific measure of site productivity and management options, reported as the height of dominant and co-dominant trees (site trees)in a stand at a base age such as 25, 50 and 100 years Stocking – a quantitative measure of the area occupied by trees relative to an optimum or desired level of density which varies according to management purpose even on the same site Stand Density Index – a measure of the stocking of a stand of trees based on the number of trees per unit area and DBH of the tree of average basal area Volume table – a chart based on volume equations that uses correlations between certain aspects of a tree to estimate the standing volume Stand density management diagram – model that uses current stand density to project future stand composition Units of measurement Cord – very common measure, equivalent to 128 cubic feet (3.62 m3), corresponding to a pile of wood,