Question: what area is zone 1?
Answer: Old Street, Angel, Pimlico, Tower Gateway, Aldgate East, Euston, Vauxhall, Elephant & Castle, Borough, London Bridge, Earl's Court, Marylebone, Edgware Road, Lambeth North and Waterloo are in zone 1 but not in or on the Circle line. Every London Underground line has stations in zone 1.