The majority of the population resides in the coastal area, particularly in two cities: Santander, with 183,000 people, and Torrelavega, the second largest urban and industrial centre in Cantabria, having a population of around 60,000. These two cities form a conurbation known as the Santander-Torrelavega metropolitan area. Castro Urdiales has an official population of 28,542, making it the fourth largest in the region because of its proximity to the Bilbao metropolitan area, there are a large number of people not registered in Castro Urdiales, and the true count may be double the official figure.