Iím not a satellite navigation specialist but here is what I know about GPS and POIs.
GPS or Global Positioning System is a navigation system using satellites to pinpoint the location of a GPS receiver through a trilateration method. For example when you open your GPS unit, it links itself to various satellites. One satellite will say to itself: "marcopolo is somewhere around here". A second one will say: "I think he is rather here". A third one will believe that you are over there. The intersection (trilateration ) of all three measurements, the result, will be your real location with an acceptable degree of error. More at Wikipedia :
[url=http://en.wikipedia.org/wiki/Global_Positioning_ System]Global Positioning System[/ url]
A POI is a Point Of Interest meaning the description and the spatial reference or coordinates (Latitude, Longitude) of the location of a specific place such as a city, campgrounds, parks, hotels, garages, gas stations, fixed radars, etc. These POIs can be uploaded on certain mobile units such as PDAs, GPS units (Garmin), software (Street and Trips,TomTom Navigator), even cell phones, etc. using features of the software itself, special software (PoiEdit : http://www.poiedit.com/
) or the sync software included with the unit).
If a GPS unit can locate you, it can also show you where a POI is located since it also uses latitudes and longitude data. Your GPS unit can then create a route between your actual location and the POI you want to get to. Microsoft Street and Maps is probably the most popular navigation software available. This kind of software will trace your route on a map and follow you as you move telling you if your are off route or not. GPS units such as those of Garmin (http://www.garmin.com/automotive/pro...tml#automotive
) or Magellan (http://www.magellangps.com/
) also have similar features. The choice between a handheld unit and a piece of software depends on your needs (road traveling, hiking, boating).
Hope this helps you a little.