(1) (Data West Research Agency definition: see
GIS glossary.) The closeness of results of observations, computations, or estimates of graphic map features to their true value or position. Relative accuracy is a measure of the accuracy of individual features on a map when compared to other features on the same map. Absolute accuracy is a measure of the location of features on a map compared to their true position on the face of the Earth. Mapping accuracy standards generally are stated as acceptable error and the proportion of measured features that must meet the criteria. In the case of some plotting and display devices, accuracy refers to tolerance in the display of graphic features relative to the original coordinate file.
(2) (Data West Research Agency definition: see
GIS glossary.) The level of allowable error of maps, as applied by National Map Accuracy Standards, is determined by comparing the positions of well-defined points whose locations or elevations are shown on the map with corresponding positions as determined by surveys of a higher accuracy. The accuracy of any map is equal to the error inherent in it as due to the curvature and changing elevations contained in each map from which the map was made, added to or corrected by the map preparation techniques used in joining the individual maps.