Sorry Jason, didn't mean to confuse you: I am not an expert on this, but here goes:
The difference pertains to the A-GPS vs GPS technology. The A-GPS (assisted GPS) is typically used in mobile phones, while GPS is used in more commercial applications (true GPS units, aircraft, ships, etc).
Traditional GPS links up directly with satellites to communicate data.
A-GPS makes use of cellular towers (or wifi) to relay satellite data and usually can be quicker to detect and give you a location. However, in areas where you have a weak cellular signal, navigating by one will be compromised. The A-GPS will utilize the cell towers to sort of "cheat" to determine location and provide a quicker response, whereas pure GPS will need to triangulate with three satellites assuming line of sight, which can and often does take a couple of minutes. Indoors or in a canyon even GPS will have issues working properly as it won't be able to "see" the satellites.
There are some mobile phones using A-GPS which can also directly link up to a GPS/satellite network as a backup, but for now, these are more likely to be the
exception not the norm.
Both technologies can work great in certain situations, though both are also subject to transmission signal strength, having obstacles blocking signals and of course rely on batteries to function. Carriers also occasionally shut down GPS at times.
In urban or suburban areas (ie areas where your carrier's cell towers are plentiful and signal strength is strong), A-GPS works great even where there are a lot of buildings around (and where line of sight would be hard to get for GPS-AGPS can use cellular towers to overcome this limitation) . In more remote areas or open areas, traditional GPS seems to have the edge, for now.
Think about those spots where you're cell phone won't work because it cannot find a signal (such as sparsely populated regions on earth). In those places, the A-GPS will also be hard pressed to work properly.
In either case, you are still relying on batteries working, which when dead, you are holding a fragile paperweight and extra weight in your pack. I don't recall seeing any wifi hubs on Whitney.
Hope that helps.
