IPhone GPS general information

Question

Apple, please contradict if this accurate.
This is not a complaint, just general information as I understand it. However, many people on complaint threads appear to be confused about whether or not their unit is using satellite GPS. This is an attempt to give information for anyone who wants to know about GPS. It is NOT official.
I have both a dedicated GPS (Garmin) and an iPhone 3G.
While the dedicated GPS only works if it can pick up satellite signals, the iPhone can get your location approximately if it cannot pick up the satellites (you're indoors).
In both cases your blue dot on Maps will be surrounded by a light-blue circle indicating that your fix is approximate.
If WiFi is on it will use the nearest WiFi station - even if you're indoors It can do this because there's a database called SkyHook that maps installed WiFi stations to their location. One person on a complaint thread said that "he" was getting located some miles from his present home. He had moved lately, so it makes sense that the SkyHook database hadn't been updated with the new location.
If WiFi is off and you've got some sort of cell service (and can't "see" the satellites) you can still get a location from the nearest cell tower, but it will be less accurate still.
With approximate signals like these, Maps will display a plain blue dot that doesn't do anything special. If you soom in close enough, Maps will shoe the light-blue circle to indicate that it thinks you're in the area under the circle.
The dot will also "jump" from place to place as you move closer to another WiFi station or cell tower.
If your iPhone actually sees satellites, the blue dot will appear to "send out rays" and will move in a fluid fashion along your route.
NOTE ABOUT SEEING SATELLITES: When you first go outdoors, even a dedicated GPS will take a few minutes to locate you. These units may say "Acquiring satellites" until they get a good fix. Trees, tall buildings, and perhaps heavy cloud over will prevent any GPS from seeing enough satellites to get a fix, so that the location shown on any unit or an iPhone might jump from place to place if it can't see enough satellites to get a fix.
DISCLAIMER. I have an iPhone 3G and don't appear ever to get a satellite based fix. The unit used to get good fixes regularly, so that the problem could be due to something else such as a hardware failure or a problem with the 3.0 version of iPhone firmware. A number of solutions have been suggested, and some have worked for some people; it happens that none of them yet have worked for me.

Answer 1

Thanks, everyone, for clarifications. I hope I haven't added any mis-or dis-information.
To add lne item: Motion has a free version of its software called MotionX GPS Lite, CroftUK, you can download it and read the FAQ that w7ox refers to.
That app will tell you what kind of GPS reception you're getting.
Thanks to ShadyMac for the feedback form. I will also search the Apple Knowledge Base in addition to the discussions. If I find a useful article I'll plst its number and title on this thread.