Lancashire:

Lancashire is smaller than its historical extent following a major reform of local government. In 1889, the administrative county of Lancashire was created, covering the historical county except for the county boroughs such as Blackburn, Burnley, Barrow-in-Furness, Preston, Wigan, Liverpool and Manchester. The area served by the Lord-Lieutenant (termed now a ceremonial county) covered the entirety of the administrative county and the county boroughs, and was expanded whenever boroughs annexed areas in neighbouring counties such as Wythenshawe in Manchester south of the River Mersey and historically in Cheshire, and southern Warrington. It did not cover the western part of Todmorden, where the ancient border between Lancashire and Yorkshire passes through the middle of the town.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". Where is the ancient border between Lancashire and Yorkshire located?
the western part of Todmorden