Quoted from Deez:

GPS has to have a view of the sky to work. This isn't a good solution. It'll just lock onto the last time it was powered up with a view of the sky.

Quoted from Deez:

As a rule of thumb yes. The building will attenuate the GPS signal and if your device miraculously locks on, it'll be inaccurate due to the signal bouncing off the surfaces.
Like others said, an Iphone or other device will use multiple techniques including the accelerometer to supplement the GPS.

Quoted from calvin12:

its not about optics, its about a relatively weak signal that does not penetrate steel and concrete well. have fun using a gps in downtown chicago. The concrete canyons make it hard to get good signals even in the streets. WAAS enabled GPS is better when the LOS conditions are poor though, but still not perfect.

Quoted from calvin12:

yeah it pretty much is. its right in the operating directions for most units, this is from garmin: acquiring GPS Signal 2. if necessary go outdoors to an open area, away from trees and tall buildings.
from tomtom:
Your device must be used outdoors, in an open area without tall buildings or trees too close to where you are.
Your device must have a clear view of the sky
Your device must find a minimum of four satellites.
not every manufacturer by any means but they all suck inside of buildings. The heavier the building the worse they get. wood frame house, might be ok, concrete or steel building, iffy at best.

Quoted from calvin12:

yes it is, you drop it. take any gps you have outside look at your signal strengths, take the same unit indoors your signal will drop. take it into the basement away form any windows its gonna drop more. actually if your unit will map the signals, move around and watch signals drop as the sats get hidden by obstructions even outdoors. sitting in my office right now in a old concrete building 4 feet from a window I can get 4 satellites which will drop to 0 and them go back as high as 4. if i move the unit to the window I get 9 solid.