The entrance cost (F) of a visit is fixed (the same) for all visitors. However, the travel cost of a visit will depend upon how far away the visitor lives. The further the visitor lives from the site, the greater will be her travel cost. Potential visitors from far away thus face a higher price per visit than nearby residents. By examining the number of trips taken by people who are close versus far from the site, one can estimate the demand for visits to the site