History and variable terrain have contributed to the diversity of Chinantec settlement patterns—notably, congregated, semicongregated, and dispersed. Each town has a number of smaller, dependent hamlets, which are abandoned when their soil becomes exhausted. Settlements range in size from town centers of about 1,000 to hamlets of just one nuclear family. Some larger communities are subdivided into corporate, exogamic barrios that control lands, milling machinery, and religious chapels. Only in the lowlands do towns follow the standard Spanish grid pattern. Although most highland houses possess an adjoining garden plot, they lack obstructing hedges or fences. Lowland houses are rectangular and windowless, with doors at both ends, wooden posts, and thatched or tin roofs. Highland houses are also rectangular but have windows. They are generally adobe with tile or tin roofs, although some are concrete.