Programming assignments are easy to plagiarize in such a way as to foil casual reading by graders. Graders can resort to automatic plagiarism detection systems, which can generate a “distance” matrix that covers all possible pairings. Most plagiarism detection programs then present this information as a simple ranked list, losing valuable information in the process. The Ac system uses the whole distance matrix to provide graders with multiple linked visualizations. The graph representation can be used to explore clusters of highly related submissions at different filtering levels. The histogram representation presents compact “individual” histograms for each submission, complementing the graph representation in aiding graders during analysis. Although Ac’s visualizations were developed with plagiarism detection in mind, they should also prove effective to visualize distance matrices from other domains, as demonstrated by preliminary experiments. Categories and Subject Des...