Optimization of two-dimensional thin-layer chromatographic separation often relies on selection of the two most orthogonal chromatographic systems which best co-operate in the separation. This is mainly achieved by investigating the correlation between RF values or scoring the distances between the spots. This paper presents and discusses another approach, based on the distances to the closest spot and to the top or bottom of the plate. The theory arises from a well-known geometrical problem about equal-spreading of the points inside a unit square. Two coefficients are proposed — sensitive and insensitive to complete separation, which are the two-dimensional version of previously proposed RU and RD criteria (retention uniformity and retention distance, describing the equal-spreading of the spots in one-dimensional chromatography). They are included in the range 0–1 and their distribution as a random variable is well defined and not affected by the number of separated compounds.