Iran is divided into 28 ostans (provinces), each headed by a governor-general; the governor-general and district officials of each province are appointed by the central government. The ostans are subdivided into sharestans (counties), which are in turn divided into bakhsh (districts). Each bakhsh consists of two or more dehistans , which are composed of groups of villages or hamlets. Each of the municipalities ( shahrdarys ) is headed by a mayor. Some sharestan officials are elected; others are appointed by Tehran.