Until recently, people lived mostly in villages with populations between 50 and 3,000 on the outer islands. Most houses are made of materials obtained from coconut and pandanus trees. Frequent droughts and infertile soil hinder reliable large-scale agriculture, so the islanders have largely turned to the sea for livelihood and subsistence. Most are outrigger sailors and fishermen. Copra plantations serve as a second source of employment. In recent years, large numbers of citizens have moved to the more urban island capital of Tarawa, where Betio is the largest town and South Tarawa reunites larger towns like Bikenibeu or Teaoraereke. Increasing urbanisation has raised the population of South Tarawa to 63,017.