The Netherlands is a parliamentary constitutional monarchy with a unitary structure. It has a land area of 33,500 km2 (12,900 sq mi) with a population of 17.8 million people. The Netherlands is divided into twelve provinces which are divided into 342 municipalities. There is a long tradition of drafting urban traffic and transport plans which largely correspond to the SUMP Guidelines. Larger municipalities draft a new plan every 10 years. There is no separate mobility policy as this is developed as part of a spatial and environmental policy plan.