A raster approach to population estimation using high-altitude aerial and space photographs

Abstract

In an effort to automate the time-consuming procedure of the dwelling unit count method of population estimation using aerial photographs, a raster approach was adopted to extract residential building density data on a grid cell by grid cell basis from high-altitude aerial and space photographs. The maximum possible occurrence of dwelling units in each grid cell was determined with reference to the dwelling unit sizes and existing housing data from the census. The actual percentage of occurrence of residential buildings in each grid cell was then estimated from the photographs and translated into a population estimate. This approach was applied to the Providence area, Rhode Island, using both black-and-white National High Altitude Photography (NHAP) at 1:80,000 scale and Large Format Camera (LFC) photography enlarged to 1: 50,000 scale. It was found that the number of dwelling units so obtained from NHAP had to be corrected with the application of a double logarithmic model and that tone was the sole element used in dwelling unit estimation in the case of LFC photography. At census tract level, population estimates exhibited mean relative errors between +2.50 and +6.94% in NHAP and between −8.24 and −13.64% in LFC photography, depending on whether regional or overall household size values respectively were employed in computing the population size from the number of dwelling units. The raster approach permitted the application of a microcomputer-based GIS package to model and update the population estimation from high altitude aerial and space photographs.