Some tools have been developed by the OSM community to allow the map data to be translated into the format used for maps with Garmin GPS receivers.
Mkgmap is the main OSM to Garmin converter. It reads OSM XML files and generates Garmin .img format maps based on a style definition.
The tile splitter is often necessary to pre-process large OSM files before running mkgmap. It splits the file into multiple files covering smaller areas, allowing individual maps to be generated. Creating a single map from a large OSM file will often fail because Garmin files can only contain a limited number of objects.
-- StephenCavilia - 23 Aug 2011