Garmin GPS III Plus Mobile Satellite Navigator

The Garmin GPS III Plus is no longer in production. This information is meant for second hand buyers.

The Garmin GPS III Plus does a good job at precisely locating the spot where it is, at any given time. However, the built-in map is so inaccurate that one is baffled by the immense number and size of the errors.

Since May 1, 2000, when the SA, or popularly speaking " scrambling of navigational signals for civilian usage" was turned off, the Garmin GPS III Plus is usually showing locations with a deviation of plus or minus 5 meters, which is very usable. Consequently, you can actually save waypoints, as specific points you save in the memory of the unit are called, and be expected to have it lead you close to eg. the edge of a lake, without your risking getting wet. When using an external antenna such as the Lowe, the precision frequently increases to plus or minus 3 meters, so you can actually see on the "bread crumb trail" of dots the III Plus makes every 30 seconds, which side of a road you are driving on, if you have driven on it recently in the opposite direction.

Built-in Maps - The Amphibious, Tracked Tank With Diamond Armor

If you need to use a GPS with reliable maps, then the Garmin GPS III Plus is not for you, as the maps in the units are of extremely poor quality.

When driving along a coastal road, I have been shown by the III Plus to be moving at 80 kilometers an hour, several hundred meters out at sea. Driving through towns, I regularly crash through concrete buildings at 50 kilometers per hour. When driving on the freeway from Copenhagen to Elsinore in Denmark, I'm racing along on plowed fields and through dense forest at 110 kilometers an hour. When driving up the E6 from Helsingborg to Gothenburg in Sweden, the road follows a railroad for a while. Yet the III Plus' map tells you that the railroad is in fact crossing the road at some point, and disappearing into a forest - never following the road. When sailing down the Southwestern part of the coast of Greenland, the ship, according to the III Plus, is sailing on bare rock, up to over a kilometer high, over considerable distances.

As the examples show, precision, regarding where you are in relation to where the built-in map tells you that you are, leaves a great deal to be desired. If you're totally lost, and need to find out where you are, and you are at the right map zoom level, you will be able to find the general direction of the towns around you - that is basically what the built-in map is good for.

MapSourceTM: Hidden Cost To Get Usable Maps - Maybe

Consequently, you need to buy a CD-ROM with more precise maps from Garmin, at a cost of more than $100. Still, that is not a guarantee that you will get usable maps that you can put in your unit. The III Plus only has 1.44 Mb of available space for extra maps, without the possibility to expand the available memory, so the maps on the CD-ROMs do not necessarily fit into the III Plus.

I needed to go to Los Angeles at one point, and bought the MapSourceTM Metroguide U.S.A., so I could have some maps of the area I was visiting in my unit. However, each map-part is in sizes of over 8 Mb, and consequently couldn't be downloaded into the unit. I had to resort to finding the relevant places on the map through the pc program that comes with the maps on the CD-ROM, make waypoints of them, and then download them into the III Plus, using the cable that comes with the unit, so I had something to go after. That is a pretty expensive way to get only waypoints, and no maps.

A participant of the newsgroup sci.geo.satellite-nav - a good place to get answers to your questions regarding GPS - told me that the MapSourceTM Road & Recreation CD-ROM's will give you map portions in sizes that fit into the III Plus, but that the MetroGuide will not. It is unfortunate that this is not mentioned on the cover of the CD-ROMs or on the CD-ROMs themselves, or in the description of the III Plus on the Garmin home page - on the contrary. Here is a quote from the Garmin home page description:

Simply plug it into a PC and download an extra 1.44 MB of map data from GARMIN's line of MapSourceTM CD ROM's to give you instant detailed maps.

Whether you're cruising the streets or pounding the waves, GARMIN has the maps you need. Choose the "U.S. Roads and Recreation" CD for city street level detail and even inland marine features such as lake and river shorelines, boat ramp and marina locations. Other CD's give you worldwide coverage of coastlines, including a database of coastal cities, navaids and inland roads.

The manual states on page 33:

The GPS III+ features a powerful real-time moving map...

One can wonder about the "powerful" part. Hopefully it isn't map precision that is meant.

So - if you need a rugged GPS unit, which, I believe, is tested to be able to spend 30 minutes under 1 meter of water without harm, and have no need for built-in maps, then the Garmin GPS III Plus is excellent. Otherwize, try other products.