Connecting historical and contemporary small-area geography in Britain: the creation of digital boundary data for 1971 and 1981 census units

This paper reports on the outcome from a project that has developed a GIS-based procedure to capture digital boundaries for the small spatial units used in the British Population Census in 1981, and for the geographically comparable units connecting back with the previous enumeration in 1971. 1981 census geography was originally recorded as linear and textual annotations on paper base maps that were subsequently microfilmed. Four methods involving varying degrees of automation for capturing digital representations of these census units from the scanned microfilm imagery are evaluated. Details presented are in the context of British census geography before digital capture of small census units became routine, but the evaluation of the methods and the final procedure cover issues that are generally applicable in situations where the capture of historical mapping is attempted.