In article , Richard J.
writes
Yes, Northfields and South Ealing are the stations,
on the Piccadilly Line. They are only 0.48km apart.

It's the distance quoted in CULG, and is probably an official LUL
distance, but I can find nothing on the site which indicates where such
distances are measured from. Perhaps Clive can comment?

Those are normally taken at the mid-point of the station, though termini
may be the buffer stops instead.

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