The 201 inhabited islands are the larger or best fishing Islands. Houses are made of local vegetation and thatch or coral stones, sometimes with imported iron or tile roofs. People desire pleasant houses, and they often arrange them on streets with the plots marked by stick fences. The island is the social and administrative unit. Everybody has official registration on his or her island and cannot change it to another Island without twelve years' residence. Each island comprises an insular social community, in which its land, people, and products are preferred to those of other islands. The islands are grouped into nineteen administrative atolls. Male is the only city, with some multistoried buildings of coral stone neatly whitewashed and mostly built along the straight sandy streets. It has a pious air, with thirty-five mosques and many tombs. Nearby is the airport island of Hulule, with a runway extending on the reef. Some 60 "uninhabited" islands are now built up as profitable tourist resorts, which especially attract Europeans in winter, but the government tries to minimize their cultural influence.