Urban population densities refer to the concentration of people living within a specific area of a city or urban environment, often measured in terms of the number of individuals per square kilometer or mile. These densities can significantly impact urban planning, infrastructure development, and land use decisions, shaping the social, economic, and environmental dynamics of urban areas. High population densities often lead to challenges like overcrowding and strain on resources, while low densities may result in underutilized spaces and increased transportation needs.