According to the ASPRS Positional Accuracy Standards for Digital Geospatial Data, the terms positional error and absolute and relative accuracy are defined as follow:
- Positional error – The difference between data set coordinate values and coordinate values from an independent source of higher accuracy for identical points.
- Positional accuracy – The accuracy of the position of features, including horizontal and vertical positions, with respect to a horizontal and vertical datum.
- Relative accuracy – A measure of variation in point-to-point accuracy in a data set.
- Relative accuracy – Characterizes the internal geometric quality of an elevation data set without regard to surveyed ground control.