GraphHopper is a fast Open Source road routing engine written in Java. It uses OpenStreetMap as data source and implements road routing via Dijkstra algorithm and variations. To make shortest-path calculations in under 50ms possible - even for paths of continental length - GraphHopper uses a special "shortcut-technique".

In this talk I'll give you a brief summary of the internal graph representation and how to scale this to gigabytes of memory and still make it running on Android. Including a short overview of Dijkstra, the memory efficient graph traversal API and how to map the real, geographical world with GPS coordinates and roads into a mathematical graph representation with edges and nodes.