Areal interpolation is a geospatial analysis method that allows researchers to estimate the incidence of a phenomenon in one set of areal units given data based on different areal units. One practice implemented in conjunction with areal interpolation is known as filtered area weighting, in which ancillary data is introduced to exclude specific areas from the areal units based on certain criteria, thus providing a more accurate representation of population distribution. This thesis examines the benefits that filtered area weighting can provide to population estimation using a hospital accessibility case study. The study shows that filtered area weighting does not always improve population estimation as expected, and suggests that the ancillary data and the criteria employed to exclude areas from analysis needs particular attention in future research when the filtered area weighting method is used.