Snap 1950s colour map network to 1890s B&W map

[docuracy]

Use vectors extracted from OS 7th Series coloured maps as a framework for detecting and checking the extraction of vectors from the earlier OS 6" maps. This is far preferable to using the modern network as a reference framework because it predates the widespread road-building and realignment of the 1960s and 1970s, which introduced motorways and many roundabouts.