There is a whole lot involved like softwares, communication protocols involved and assigning a physical location with some kind of addressing system but it is for more technically inclined people.

The goal of this articles is to explain how gps work in a layman's voice and not to dig into technical details. Once we understand roughly how these great gadget works and operate it will be easy for us to appreciate, use and make judgment which ones to buy based on what features are available. What is the objective and how do you plan to use GPS.

With the advancement in semi-conductor technology, integrated circuits are getting smaller and smaller. Not only smaller but they are getting cheaper also. This proliferation of ICs or integrated circuits have made it possible to develop new devices and gadgets like GPS in a more economical way.

Now you will find GPS in cars, private boat and taking with them when going for trips like hiking and fishing. A GPS may be used for hiking, fishing or aviation. And has many many more uses then I can mention here.

An important thing to consider which is almost a must is to determine the usage of GPS and then compare the feature matrix between different supplier like Garmin, Lowrance, TomTom or Magellan

Some of the features you may want to consider.
Map ? to show you where you are at a given moment.
Long battery life ? the more the better
Waterproofness ? if you want to take where there is water. E.g. fishing or in boat.
Small size and lightweight ? Always a positive feature in my opinion.
Built in maps.
Waypoint ? must have 500 or more.
GPs with integrated traffic. Subway and train schedule

Once you decide what features you want then only compare the prices as what good a GPS is if it does not have what you were looking for.