ABSTRACT
In certain situations, geographical data may be obtained from secondary sources such as existing maps, tables, or other databases. In other situations, primary data may be derived from measurements conducted on the spot or via remote sensors. Awareness of data accuracy requires that assessment be made of the instruments and procedures used for measurement and data compilation, and also that measures of resolution, accuracy, and other indicators should be included in the data documentation, in other words should be recorded in metadata. Land or soil surveyors are trained to be concerned with inaccuracy when they perform measurement and sampling, and methods of data reduction, such as least squares, provide measures of accuracy in addition to the best estimates of true values.
