Route-Me is an open source map library that runs natively on iOS. It's designed to look and feel much like the inbuilt iOS map library, but it's entirely open, and works with any map source.
Currently, OpenStreetMap, Microsoft VirtualEarth, CloudMade, OpenAerialMap, OpenCycleMap, SpatialCloud, TileStream7, and two offline-capable, database-backed formats (DBMap and MBTiles) are supported as map sources.
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