This site provides replacement maps for Garmin Nuvi series devices. The maps will also work on handheld Garmin devices (eTrex, Oregon, Dakota, Colorado, Montana, Colorado, GPSMAP 62) and the older Garmin StreetPilot devices if the device has an SD Card slot.
The maps are created using map data provided the OpenStreetMap project, a user-editable map of the world. Like all maps, the maps provided by this site might have some errors. You are encouraged to fix any problems you find directly in OpenStreetMap. Simply navigate to the area you would like to update and click the "Edit" button near the top of the page.
The maps on this site are refreshed biweekly so that users can benefit from fixes and updates without much delay. The maps are created using the mkgmap map compiler. You can create your own maps by following the mkgmap map creation guide.
OpenMapChest is one of several projects that I have created. Feel free to browse my other projects to see if there's something else useful for you.