Correlation lines, connecting two undisturbed sections in the same geological province have a distant intersection, which lies on the shoreline of the basin. This configuration closely approaches a perspectivity. In projective geometry, perspectivities are governed by simple cross-ratio equations. In the ideal case they are also applicable to two strings of correlative borehole markers. Departures from the perfect geometric model are discussed and geologically interpreted. Since cross-ratios are fractions, the denominators and divisors may be reduced proportionally. Thus by drawing one section on twice the scale of its mate, a graphical solution may be obtained within the bounds of a sheet of typewriter paper.

Although perspective correlation has mainly been tried out in the Western Canadian sedimentary basin, this method should be applicable anywhere in the world to other, largely marine basins that have not been too severely disturbed by post-depositional structural movements.