1. A method for determining categories for a set of source data, comprising: obtaining a set of source data using a distributed data categorization server system, where a piece of source data comprises source data metadata describing attributes of the piece of source data; determining a plurality of subsets of the source data using the distributed data categorization server system, where a subset of the source data comprises a plurality of pieces of source data in the set of source data; generating a set of pairwise annotations for the pieces of source data in each subset of source data using the distributed data categorization server system, where a pairwise annotation indicates when a first piece of source data in a pair of pieces of source data in the subset of source data is similar to a second piece of source data in the pair of pieces of source data; clustering the set of source data into related subsets of source data based on the sets of pairwise labels for each subset of source data using the distributed data categorization server system; and identifying a category for each related subset of source data based on the clusterings of source data and the source data metadata for the pieces of source data in the group of source data using the distributed data categorization server system.