This shows the relationship between the distance and the population density from a central point. It is the graphical technique which shows the rate of decline of population density with increasing distance from the central point of concentration.
The rate at which population density declines with increasing distance from a central is known as population density lapse rate. The relationship between population density and the distance from the central point is inverse (negative exponacial relationship). The steepness of the curve indicates the rate of decline. The steeper the gradient of the curve, the faster the decline and the more gentle the gradient? the slower the decline