1. A computer implemented method of identifying reference data likely to match target data, the method comprising: reading a reference set of summaries of data included in a reference 5 data set, each member of the reference set of summaries including a plurality of summaries that indicate particular patterns of the reference data within the reference data set; comparing the reference set of summaries to a target set of summaries associated with at least one target area of a plurality of target areas, each member of the target set of summaries including a plurality of summaries that indicate particular patterns of the target data included in the at least one target area, the plurality of target areas being included in a target data set; and associating the at least one target area with the reference data set when a threshold number of members of the target set of summaries associated with the at least one target area match members of the reference set of summaries.