Complex sentence: Municipal police are authorized in every town and city of 5,000 or more people, and the Policía Municipal de Madrid is the largest such force and the Guàrdia Urbana de Barcelona is the second largest.
Split into simpler sentences: Municipal police are authorized in every town and city of 5,000 or more people. The Policía Municipal de Madrid is the largest force and the Guàrdia Urbana de Barcelona is the second largest.