Tuesday, October 18, 2016

Distribution Visualization Tools in Nomisma.org

I have spent the last month working on and off on a new set of research tools in Nomisma.org's interface. As users of individual ANS type corpus projects (like OCRE) will know, we have exposed simple weight and diameter analyses and the distribution of typological categories (like denomination, mint, authority, etc.) as graphs through a visualization interface. These interfaces query only those coin types or physical specimens connected with the type corpus as a whole. Plainly, this means that the interfaces in OCRE only query coin types from RIC or display the average weights of coins that have explicitly been connected to URIs published by OCRE. Partners with find or excavation databases that contain uncertain coins are excluded from these queries, even if the portrait or mint can be positively identified, but the wear of the legend is too great to allow for a certain RIC attribution.

I have begun to implement distribution visualization interfaces directly in Nomisma that query its SPARQL endpoint. At present, the distribution analyses are based on coin types. For example, you can generate a chart that shows the distribution of denominations issued by Augustus. You can place further filters on this query, for example, to show the distribution of denominations issued by Augustus at the mint of Rome. The interface allows you to gather multiple datasets for comparison, e.g., to include the distribution of denominations for Nero and Hadrian. These queries factor in all coin types, regardless of the scope of the type series, enabling you to query across all coins of the Roman Republic and Empire simultaneously.

Distribution of denominations of Augustus, Nero, and Hadrian from the mint of Rome

Some work remains in enhancing the complexity and scope of these queries. It is important to introduce start and end date filters so that it would be easier to evaluate changes in distribution over time. Furthermore, the categories for visualization (authority, issuer, mint, region, denomination, material, object type) need to be expanded to include portraits and depicted deities. This adds a layer of complexity in the query--these objects are referenced in the obverse and reverse of the coin type, not directly in the coin type data object itself. Presently, deities are an underutilized query parameter across all our projects. We use British Museum URIs, but have not integrated SKOS PrefLabels or any other properties about these URIs into the Nomisma SPARQL endpoint that would allow us to build a human-readable interface. Adding supplementary, non-numismatic datasets is on the agenda for Nomisma development.

The distribution analysis interface is available on the pages for individual Nomisma IDs (if these IDs have associated coin types) and on a separate interface. The distribution interface renders the chart by passing URL parameters to itself, so the page URL can be copied and pasted, and the charts can be shared with others. The charts on the Nomisma ID page are generated directly with ajax calls (so it is easier to view changes in the graph when modifying underlying queries), but you can click a button load the chart in the distribution page. There is an option to download the data as CSV in both interfaces.

Next: Metrical Analysis

Once I implement portraits, deities, and date filters, I will get to work on interfaces that will analyze weights and diameters. This interface will open the door to integrating physical coins that have been connected to typologies implicitly through OCRE, CRRO, and PELLA URIs or explicitly, enabling us to compare all coins of an emperor even when the specific coin type attribution cannot be ascertained.

These interfaces will not only show the average weights of typological categories, but changes in weight over time (e.g., to view the change in weight of the denarius over 400 years). I'll also implement standard deviation visualizations to cluster coins together of nearly identical weights, making it easier to spot outliers that might be fragmentary coins or even forgeries.

No comments:

Post a Comment

Note: Only a member of this blog may post a comment.