A system for improving the accuracy of location coordinate determined in a survey of a chosen region, using a computer. A grid of spaced apart points is imposed on the region, and a set of survey control points is provided. A "near set" of nearest survey control points is associated with each grid point. For each grid point, a transformation T from a first (global) datum and coordinate system to a second (local) datum and coordinate system is determined that minimizes a collective difference between coordinates of each survey control point in the near set and the corresponding coordinates of that survey control point under the transformation T. For one, two or three coordinates of each grid point, a difference .DELTA. between the coordinate(s) of the grid point in the near set and the corresponding coordinate(s) of that grid point under the transformation T is computed. An interpolation function is determined that approximately matches the coordinate(s) difference .DELTA. at each grid point. The interpolation function provides a continuous datum-to-datum mapping between all points of the first and the second coordinate systems. Determination of location of each survey point may use GPS, GLONASS, modified LEO, LORAN or any other suitable location determination system.