You can update mapping software on most sat nav units to take into account alterations to the road network. Either from your PC, in the case of portable sat navs; or via your phones GPRS connection, in the case of phone models. Always check the level of mapping that comes with your equipment in the first place. Is it up-to-date? Does it have UK street level mapping? European major roads? European street level mapping? North American roads? Ensure you have the right mapping before you buy.