Ernest R. Mowrer

The Isometric Map as a Technique of Social Research

Cross-hatching as a device for showing variations in the rates of social phenomena from community to community give the erroneous impression of abrupt changes in rates at the boundaries of areas. The spot-map, on the other hand, potrays an ecological distribution more realistically but at the sacrifice of the population base. What is needed is a technique comparable to the relief map in geography in which altitudes are portrayed by countours. The isometric map technique performs that function. Convenient points in the range from the highest to the lowest rates are represented by isometers calculated by interpolation. If the areas for which rates are available are comparatively large, the geographers method of interpolation can be used directly. If the areas are small, it is necessary first to calculate corrected rates for which a formula is provided. In either case the distribution can be made more graphic, one the isometers have been drawn, by cross-hatching appropriately the areas bounded by each pair of isometers. The result is a portrayal of variations in rates which suggest continuous movement instead of the abrupt changes characterizing the conventional cross-hatching procedure. Furthemore, if it is desired to superimpose one series upon another, this can be done through the used of the isometric technique, thus revealing graphically the correlation between the two spatial distributions. The validity of the isometric map technique has been checked by calculating the Pearsonian coefficients between two series: first, by the use of city blocks as units, and, second, by measuring the areas circumscribed by pairs of isometers. In all the test cases the paired coefficients have been substantially same, demonstranting the validity of the isometric technique.