Two basic rules for valid contouring
W. E. Sharp · OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information) · 1987
For automatic contouring to be valid using digital data, two very specific rules must be observed. The data must show spatial persistence out to the second nearest neighbors. The contour interval must be selected so that the probable error of any point value does not exceed one-half of a contour interval. If the second rule is strictly observed even random data can be correctly contoured. If Rule 1 does not hold, the data still can be displayed but only as a dot map.