After five years of work, our wonderful team of student researchers has put the finishing touches on the Digital Atlas of Dioceses and Ecclesiastical Provinces in Latin Christendom (1200-1500)! All of the mapping files and their associated documentation can now be downloaded here, and are available for public use under a Creative Commons license.
The maps are necessarily limited by the constraints of source survival and the state of existing scholarship. It proved impossible to depict the ecclesiastical geography of the Latin East (with the exception of Cyprus), and the boundaries of many jurisdictions in eastern Europe are pretty vague (no doubt this was true in reality as well!). In other parts of Europe (notably Iberia and parts of central Italy), a certain amount of conjecture was necessary to deal with shifting boundaries and contested jurisdictional claims.
We welcome comments, corrections, and suggestions for future updates!