Various methods have been employed by geologists to determine the similarity of spatial data represented by contour maps. These methods generally entail the separation of specified components within the map surface. Visual comparison of maps was the only method possible until introduction of computers when automated quantitative techniques became available.
Polynomial trend-surface analysis was introduced in the late 1950s and early 1960s to separate regional and local components of a data set. Miller (1964) suggested direct comparison of the computed grid matrices as a method of map comparison. A matching coefficient for comparison of trend-surface anomalies was used by Merriam and Lippert (1964). Merriam and Sneath (1966) used the coefficients of the calculated polynomial trend surfaces as numeric descriptors for comparison. Another method of comparing surfaces involves rearrangement of the least-squares summation equations for direct comparison (Rao, 1971).