Accuracy The positional accuracy of spatial data is the degree to which planimetric coordinates and elevations of features agree with their real world values. The planimetric accuracy will be composed of errors from three sources: The positional accuracy of the source material Errors due to conversion processes. Errors due to the manipulation processes. Absolute horizontal and vertical accuracy will vary by location according to the source data. Absolute accuracy is defined as the difference between the stored coordinates and the true coordinates for a specific point. For horizontal accuracy, 90% of points will be within 2km of their actual location. In the case of data obtained from satellite images, the maximum error is less than or equal to 0.5km. Vertical accuracy is notionally 150 metres for 90% of points. This figure may need to be reviewed once the data are available, as sources to this accuracy may not be available in areas of high relief.
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