192 Surfaces 
6.2 Surfaces and Gradient, Maure of swfaces Whether we regard phenomena as a series of discrete points in space, or whether we generalize them into a continuous density surface, depends very much upon the degreeof spatial generalization that we are prepared to accept. As we demonstrate in Chapters 10 and 12. spatial pattern is largely a function of thescale at which we look. Like height contours on a topographical map, we can regard lines of, say, equal population density as demographic contours. This surface may be thought of statistically as a response surface, in which