Garmin has been talking about its landmark-based navigation Real Directions ("Turn right at the McDonalds") for some time. The NY Times reveals some of the challenges the company and partner Nokia (NAVTEQ) found in building the solution, now available for 52 U.S. cities:

In test drives, a team of employees from Garmin and from the Navteq mapping division of Nokia discovered that the direction of travel changed what needed to be said — a landmark visible when approaching from the north might be hidden when driving from the south. Tests also found that drivers became puzzled if they were told to turn right when the landmark was on the left.

What that meant, from a practical sense: collecting far more landmarks that exptected. And, I'll offer, keeping all those landmark descriptions up to date. If the McDonald's becomes a Wendy's, that'll need updating.

- NY Times