This paper concerns the problem of matching incompatible zonal geographies, for example in the context of comparing census outputs over time. The automated zoning procedure (AZP) proposed by Openshaw (1977) is reviewed and extended to permit its application to the intersection of two zonal systems. A population stress statistic is proposed which may be used in the extended AZP algorithm in order to maximise the match between two zonal geographies. An implementation of this approach is described, and illustrated by reference to UK Census data.