Estimating census district populations from satellite imagery: some approaches and limitations
Small-area population densities and counts were estimated for Australian census collection districts (CDs), using Landsat TM imagery. A number of mathematical and statistical refinements to previously reported methods were explored. The robustness of these techniques as a practical methodology for population estimation was investigated and evaluated using a primary image for model development and training, and a second image for validation. Correlations of up to 0.92 in the training set and up to 0.86 in the validation set were obtained between census and remote sensing estimates of CD population density, with median proportional errors of 17.4% and 18.4%, respectively. Total urban populations were estimated with errors of +1% and-3%, respectively. These results indicate a moderate level of accuracy and a substantial degree of robustness. Accuracy was greatest in suburban areas of intermediate population density. There was a general tendency towards attenuation in all models tested, with high densities being under-estimated and low densities being over-estimated. It is concluded that the level of accuracy obtainable with this methodology is limited by heterogeneity within the individual CDs, particularly large rural CDs, and that further improvements are in principle unlikely using the aggregated approach. An alternative statistical approach is foreshadowed.