When Alan Turing was born, his father Julius Mathison Turing was posted at Chatrapur, also spelled Chhatrapur, in India. At the time, the town was part of the Madras Presidency; it is now in Odisha.
Julius served in the Indian Civil Service under the British Raj. He was on leave in Britain when Alan was born in Maida Vale, London, on 23 June 1912. The posting explains why Turing's birth took place in England even though his father's career was based in India.
The location is easy to confuse with major Indian cities such as Madras, Mumbai, or Kolkata. Madras was the presidency's administrative capital, but Chatrapur was the specific place associated with Julius Turing's posting. Modern references commonly use “Chatrapur,” while “Chhatrapur” is an accepted variant spelling used for the same town, so the stored answer identifies the correct place.