Samenvatting
This paper focuses on the possibilities the "qualitati calculus" may offer for spatial research. Attention will be paid in particular to the so-called sign-solvability problem. This concerns the question as to whether, and under what conditions, the direction of changes in a set of dependent variables may be determined solely from the direction of changes in the independent variables and a knowledge of the signs, but not the magnitudes, of the relevant partial derivatives.