The computer program MapAnalyst allows a fit of a test map to a standard map by a bi-dimensional linear regression on a set of corresponding points in the two maps and provides as one output the scale of the
test map, assuming that the scale of the standard map is known. Another output is a distortion grid. It is
shown by consideration of a specific example, Robert Saxton’s map of Manningham, dated 1613, that the
standard deviation of the errors in area of plots of land shown on the test map cannot be reliably determined from the distortion grid. It can, however, be determined from the statistics of the errors in separations of the points on the test map, which can be calculated from the rescaled map. The result is only reliable provided that corresponding points can be found on the two maps such that their mean separations
are comparable with the linear dimensions of the plots whose areas are considered.