Austria is a federation of nine provinces, one of which is the capital, Vienna, the most populous city and province. Austria occupies an area of 83,871 km2 (32,383 sq mi) and has a population of 9 million. Austria is quite advanced in fostering the implementation of mobility management measures in urban areas. It is not compulsory for Austrian cities to have a SUMP in place; the implementation of a SUMP is voluntarily. Some cities have compiled transport plans which include certain elements and/or variations of the SUMP approach.