Housing is one of the government's most pressing problems. While middle-and upper-income housing is comparable to that in neighboring areas of North America, facilities for low-income groups are poor by any standard. The problem has been aggravated by constant migration from the rural areas to the cities, causing the growth of urban slums. Most new urban housing is built of cinder block and steel on the peripheries of the cities. Rural housing is primarily built of wood and roofed with zinc sheeting. Squatter settlements surround the major cities of Jamaica. According the 2001 census figures, there were 723,343 occupied private dwellings with an average of 3.6 people per household.