The article analyzes urban development in fifteen European cities, focusing on the relationship between built-up areas and population density. Over the past 20 years, the built-up areas in Europe have grown by 20%, surpassing the 6% population growth rate. This unsustainable trend has led to urban sprawl, with most new housing areas being disconnected from existing urban areas. This expansion has negative effects like increased car use and fragmentation of natural areas. The study shows that European cities have become less compact, with a trend towards decentralized land use. The cities studied can be divided into three groups based on their compactness and population density: compact cities, cities with looser structures and lower densities, and cities in between.