OK, I understand that GPSes work via triangulation from satellite signals. What I’ve never seen covered in any articles about GPSes is where all the street mapping data comes from. Collecting all this data must have been a huge amount of work, and it’s pretty detailed. How was it done?
One of the major suppliers is Navteq:
It WAS/IS a lot of work. Hence, it’s valuable (and profitable) content.
They don’t. Triangulation involves measuring angles, and GPS receivers don’t do that. Instead, they calculate the time difference between signals from various pairs of satellites. This is known as hyperbolic navigation, because a curve of constant time difference is a hyperbola (in three dimensions, a hyperbloid of rotation).
It certainly is a lot of work to collect and maintain good map data. But some of it is available for free. Here’s a link to one particulary good site.
New Yorker article from last year about Navteq and how they collect their data.
That site has data good enough for simple map display and positioning, but not for car navigation and routing. That’s where the paid map data providers are needed, such as Navteq, and the other major provider, Tele Atlas. (http://www.teleatlas.com)
Ed