A district is governed by a District Collector, who is better known as a District Magistrate (DM) in the state of West Bengal. A DM is an officer from either Indian Administrative Service (IAS) or West Bengal Civil Service (WBCS), and is appointed by the State Government of West Bengal. Each district is divided into subdivisions, except the Kolkata district, which contains urban area only, administered by Kolkata Municipal Corporation. A subdivision is governed by a sub-divisional magistrate (SDM), better known as a Sub-Divisional Officer (SDO). Other than urban units such as town municipalities, a subdivision contains 'community development blocks' (also known as "CD blocks" or "blocks"). A block consists of urban units such as census towns and rural units called gram panchayats. A block is administered by a Block Development Officer (BDO), who is appointed by the Government of West Bengal.