Population geography studies populations and their relationship to the physical environment. It analyzes population evolution, composition, and spatial distribution. Demography is the statistical study of human populations and is used to gather details about population size, density, vital statistics, and more. Developed countries use questionnaires like censuses to gather accurate population data and characteristics. Less developed countries rely more on estimates. Spain specifically uses population censuses from the National Statistics Institute, civil registries of births, deaths, and marriages, and municipal population registers. Population structure can be analyzed biologically by age and sex using population pyramids, or economically based on activity status. Natural population changes include birth and death rates, while migratory movements refer to immigration and em