Poland is a parliamentary republic covering an area of 312,696 km2 (120,733 sq mi) with a population of 38 million. The Ministry of Infrastructure has been conducting many activities aimed at encouraging cities to develop and implement SUMPs. Although it is optional for Polish cities to have a SUMP, larger centers in Poland have made an effort to develop their own plans (e.g. Kraków, Warsaw and Wroclaw). Generally, in spite of rapid motorisation growth, the implementation of SUMP principles has resulted in maintaining a high share of public transport use in Polish cities.