11. A method, comprising: receiving, for at least one website, a first plurality of data points related to each visitor of a first plurality of visitors to the website, the first plurality of data points comprising at least an identification of the visitor and an interaction of the visitor with the website; performing, using a computing device, a clustering algorithm that generates a plurality of clusters using the first plurality of data points as input, each cluster of the plurality of clusters defined by a number of unique visitors and at least some of the unique visitors sharing at least one interaction in common; generating, for each cluster of the plurality of clusters, at least one assignment rule that associates a behavior common to at least some of the unique visitors in the cluster with the cluster; providing the at least one assignment rule to an updating process that assigns each visitor of a second plurality of visitors to the plurality of clusters using the at least one assignment rule; and providing the plurality of clusters to a targeting process that generates a similarity audience formed of at least some of the clusters and provides, via electronic transmission, at least some members of the similarity audience with digital content.
13. The method of claim 11 , further comprising: receiving, for at least one website, a second plurality of data points related to each visitor of a third plurality of visitors to the website, the second plurality of data points comprising at least an identification of the visitor and an interaction of the visitor with the website; assigning each visitor of the third plurality of visitors to at least one cluster of the plurality of clusters using the at least one assignment rule; re-assigning at least some visitors of the first plurality of visitors to at least one cluster of the plurality of clusters using the at least one assignment rule; determining whether to replace the plurality of clusters; and upon a determination to replace the plurality of clusters: performing the clustering algorithm a second time using the second plurality of data points and the first plurality of data points associated with the at least some visitors of the first plurality of visitors as input; and providing, to the targeting process, the plurality of clusters generated by performing the clustering algorithm the second time; otherwise: providing, to the targeting process, the plurality of clusters after the assigning and the re-assigning.