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Comment by baltoo | Hacker News Reader

Dunno, but from the top of my head: one-way streets, no-left-turn-allowed-here-signs, prolonged roadworks. Perhaps the map data doesn't even map up actual streets that well (does this road go over that one, or is it the other way around?).

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But Google Maps can already provide directions from A to B, and these factor in one-way streets, etc., so Google should already have that data, right?

Apparently they used to buy that data from the big two.

http://googlemapsmania.blogspot.com/2008/09/google-maps-drop...

Another example of data usually missing - speed limits.

My uncle from Germany who visited me last month showed me his Garmin GPS -- it reported speed limits instantaneously. Anyway, tagging speed limits with roads is one of the less difficult things in computing turn-by-turn directions, I would guess. It's just a matter of getting the data from whatever branch of gov't that has it -- (out of curiosity - if anyone knows, do tell, who exactly would be queried for such data? And what would be the logistics of it? Only acquirable for a certain fee?).

Most governments other than the US charge enormous amounts of money for map data, with very tight restrictions on licensing. Many consider it a state secret, and won't sell the data at all.

My TomTom has that data for most places, and I'm from America. I think it just depends on the GPS model and the data provider.

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