The Piccadilly extension to Hatton Cross and Heathrow Central had opened in 1977. London Transport - Underground diagram of lines - No. 1 1978 - Heathrow Central now open [10.77/2772M/1,000,000]. Title of map:'London Transport - Underground diagram of lines - No. 1 1978 - Heathrow Central now open [10.77/2772M/1,000,000]'.
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