From the site:
ORBIS: The Stanford Geospatial Network Model of the Roman World reconstructs the time cost and financial expense associated with a wide range of different types of travel in antiquity. The model is based on a simplified version of the giant network of cities, roads, rivers and sea lanes that framed movement across the Roman Empire. It broadly reflects conditions around 200 CE but also covers a few sites and roads created in late antiquity.
The model consists of 751 sites, most of them urban settlements but also including important promontories and mountain passes, and covers close to 10 million square kilometers (~4 million square miles) of terrestrial and maritime space. 268 sites serve as sea ports. The road network encompasses 84,631 kilometers (52,587 miles) of road or desert tracks, complemented by 28,272 kilometers (17,567 miles) of navigable rivers and canals.
Read more here: http://orbis.stanford.edu/.