Because A:somebody would have to go out and log exact details of the land marks, and process them into the appropriate databases. On things like GPS receivers, it would also take up memory space.B: They'd have to do it often, as landmarks get added, removed, or change hands/affiliations or appearance.

That would cost money, money that would have to add cost to a service or product.

I like this idea a lot. Memory space is becoming less of a problem. As for money, maybe the two giants that are competing in this area (Google and Microsoft) will get carried away trying to beat out the other guy and make economically irrational decisions that benefit the rest of us.

PS: Maybe in the future street signs will be outfitted with super-RFID tags that GPS systems will recognize, making navigation more foolproof & less subject to change. (Streets being more permanent than landmark-buildings and signs.)

I worked in avionics when were were expected to put all of North American in 32mb. Now you can get 4GB for $20. They gotta be able to do something with all of that space.

Also, right now, not many people buy an upgrade every-year--they usually wait until they see errors in their database. Garmin has a lucrative business in selling new updates--it's a purely intellectual property-product--no electronics to ship. The Do Really want to sell more.

Finally, turns out I'm not the first to think of this--it will be a reality in not-too-long.

I don't agree with RFID street signs ---I don't want to have every car driving around emitting high-power RF. I think that would be energy-wasteful and probably detrimental to our health too. And it's another thing on a car to break. I have old cars. I'm tired of broken stuff.

How about if the RFID plaques were embedded in roads at intersections? That way there would be much less energy needed to activate them to bounce back to the transmitter, and that energy would be directed downward--away from us.

A transponder should, if anything, be passive optical (a camera on the car will look for a tile with computer readable optical markings, which define the location enough for the GPS to understand the location), or a low power RF beacon, powered by street/traffic light power or solar panel with battery. Of course, somebody would have to pay somebody to install and maintain them.

The problem with an optical bar code is that it would be hard to read if covered by snow or oil or grime. Railroad cars have used an optical recognition system for over a decade and have had problems with some of the bar codes being unreadable due to dirt.

I don't know why you guys think the GPS needs an intersection reference at all. My GPS knows the minute I've missed an exit and it doesn't have an RFID or an optical plaque embedded in the intersection.

I assure you, if advertisers paid, the companies could keep the locations of their paid advertisers accurate--maybe they'd even give away the updates free to make sure that you have the latest ads.

You are right, if both of us came up with this idea, I hope that the mapping software people are already working on it. I just don't see why not.