Systems and methods to track the respective locations of subjects over time. The system identifies subjects who, over time, were co-located with one another suggesting they are associated with one another, and the pairs are analyzed. For each of the subjects, the system produces a vector that quantifies the subject's location history by including a respective weight for each combination of a time interval with a geographical area. The vectors are compared using a distance metric, and any pair of subjects whose vectors are sufficiently close are flagged as being an associated pair. The respective vector belonging to each subject is normalized to account for the total number of other subjects who were co-located with the subject. For each interval-area pair, the system may compute the frequency of the interval-area pair, and then divide each weight that corresponds to the interval-area pair by the frequency of the interval-area pair.
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