On a flight across Europe, I took my iPhone out to see if the GPS can find my position. I was sitting away from a window, so reception would have been bad. I wouldn't have been surprised to get no result at all, but the GPS did show roughly the location where I was, showing a circle with a radius of 100 km as the error!
How can that be? If the GPS did't receive enough satellites, I would have thought it would have no idea at all about my position, and with enough satellites received it would know exactly where I am, so how can it know my position with a 100 km error?
PS. Moving my phone to the window made it display information with tiny error bounds, and the position moving on a map at the right speed - impossible to say whether the information was correct from 10,000 meters height. And moving further to the aisle it would display that there was no reception at all. But in between it did show very roughly where I was, with huge error bounds (the software draws where it thinks you are, and a circle around it based on the estimated precision).
PS. Found an explanation, but don't know if it is correct: Even at a height of 10,000 meters, an iPhone can register signals from cell towers. It knows where these cell towers are. And knowing that there is a cell tower with a really week signal means it can determine its location with a huge error.