Richard Welty gave a presentation on OpenHistoricalMap (OHM), a project to add historical data and a time dimension to OpenStreetMap (OSM). OHM uses the same data model and software as OSM but adds support for modeling changes over time. It has a time-aware map viewer and tools for aligning historical maps and images. Current projects focus on modeling urban development, infrastructure changes, and places of historical and cultural significance. Challenges include representing time-varying data accurately and modeling historical events.