Average distances associated with radially symmetrically populated regions

The paper supposes radially symmetrically populated regions. Approximating average distances between a point and the region and between two regions are concerned. Approximate formulas are applied to the Clark’s population densities, and it has been proved that they are very accurate. In addition, beautiful structures of the average distances are derived mathematically. Those which determine the average distances are 2m-th moments of population distribution. [In Japanese.]