According to the U.S. Census Bureau, a suburb is defined as any territory within a metropolitan statistical area (MSA) that is not included in the central city or cities of that MSA. Metropolitan areas are typically defined as having at least one urbanised area of 50,000 or more people, plus adjacent territory that has a high degree of social and economic integration with the core urban area, as measured by commuting ties. Suburbs are often characterised by lower population density compared to central cities, a higher proportion of single-family homes, and a greater reliance on automobiles for transportation. They have become a significant form of residential and commercial development in many industrialised countries, often representing a migration of population and economic activity away from the central urban core. The development and characteristics of suburbs are influenced by various factors, including transportation infrastructure, housing policies, economic trends, and social preferences.