The Cassini Maps website offers digital versions of the original 1871 census maps as used by the enumerators. The maps show registrars districts & sub districts and are an invaluable aid for the genealogists searching in the 1871 census. Not all areas are available as yet, but Cassini are working on producing total coverage. Whilst on the website take a look at their other maps.
The original maps are series RG18 at The National Archives, Kew.