Demographic characteristics of a city are of a primary needs for urban decision makers. These demographic data, however are prepared or revised over long periods of e.g. about five to ten years. During these periods, the population is estimated based on subjective and approximate data like migration, along with more precise and objective data like birth and death. The result, which is subjective and imprecise data, cannot be used for deriving population distribution. Considering the need for more objective and precise estimation of population and population distribution of cities, this paper provides a spatial methodology. The premise is that the spatial characteristics of land uses and population density and population have specific relations. By defining these relations and using a precise and objective estimation of the land uses, we can project the population density and population. This methodology improves the population estimation by providing higher level of precision and objectiveness. In this paper, we introduceour findings of specific relations between land uses, e.g. settlement pattern and the human attitude to live near other human settlements and spatial continuous distribution of population. These relations are implemented in a geographical information system (GIS) using estimation-maximization (EM) approach and population density and distribution of the city Tehran, Iran is derived. The EM is used here as an area interpolation approach. The land use data are extracted from IRS-D satellite images. Besides, strategies are described in this paper dealing with the problem of lacking the spatial data.