I just came across an excellent article on how to download free maps to your Garmin Edge 705/800/810
OpenStreeMaps are easy to order from this site http://garmin.openstreetmap.nl/
and DCRainmaker tells you how to get them onto your map-capable Garmin device here:
The touchscreen Edge 810 rovides navigation and advanced training capabilities for the dedicated cyclist.
It connects through your smartphone to access live tracking, social media sharing and weather.
The 810 works with detailed street or TOPO maps for navigation when touring, commuting or doing other activities. Its GPS capabilities provide accurate data and navigation capabilities worldwide.
Read a detailed assessment of the Garmin 810