Costa Rica is divided geopolitically into a hierarchy of 7 provinces and 81 cantons. We treat each canton as an observation. Visitation rates (number of visits per 100 000 residents) were calculated for each canton by dividing observed numbers of trips by census populations. Popultions, densities, and illiteracy rates for each canton were taken from a 1986 census (7). Distances between the canton of origin and the MCFR were measured using the 1:200 000 scale conventional maps prepar- ed by the Instituto Geographico Nacional (1988 revision). Distances were measured parsimoniously along the most likely roads between the major population center of each canton and MCFR