population density• Averagepopulation densitiesdoubled between 1900 and 1960.• Where there is a high population density and a rapid population turnover, the church must achieve visibility.• He suggested that the main cause of social differentiation was the increase in population density.• Counties with low population density have sparseshading while counties with high population density have dark shading.• Ruralpopulation densities are of primeimportance in modifying the implications of the different relations of production under which land is used.• Presumably there are factors that control the size, and they depend on the population density.• The sampling frequency of water depends under regulations upon population density.