Home Earthmate StreetPilot III G3+ vs GM100 iFinder Lowrance DGPS EA3 Antenna Magellan 315 Review Magellan Map 330 Magellan Map410 review PhilSherrod Rand McNally GPS Infiniti QX4 SUV GPSGM100 vs. G3+ Side by side


The Review


Part 1 -- Challenging the Comparisons Made

We felt some of the direct comparisons that were made were overstated.Here are some comments on those:

1)      Garmin maps have 10% more street-vector resolution.

From the screen shots J&J showed in the review, there were a few vectors missing on the GM100 maps, but they had little or no effect on the readability, function, or accuracy of the maps.The elimination of unimportant vector detail frees up memory so that larger areas may by uploaded without compromising accuracy.We feel this is an advantage for the GM100.

2)      Highways and street names on the G-III+ maps are designated more often too.

We think this is misleading, at least from the screen shots that are shown.† J&J point out that the G-III+ will display street names by pointing at them and that the GM100 will not. This implies that the GM100 is not capable of displaying some street names. This is not true!

From what we can gather, the G-III+ shows its road names a little earlier in the zoom process, but the GM100 will also show them at higher zooms.In fact, the GM100 doesn't show the names of the smallest of roads / streets until you have reached a level of zoom (0.4 miles for Rural Roads and 0.2 miles for City Streets) that is appropriate for the length of the street/road on the display.If you displayed them at lower zoom levels, the letters would blend together and become unreadable.J&J complain about the G-III+ doing exactly this later in their review.

  According to  GM-100 and G-III Map Picture Comparisons (28 Jan 1999), in the following screen shots " Both GPS receivers are adjusted for the highest map resolution and detail available in all pictures." 


To get the above pix, the "LOCATIONS" option of GM100 had to be turned OFF.  The screen dumps below, show the same area with "LOCATIONS" ON; the small square dots indicate where (street and other) names show when zoomed in.


The commentary goes on to state that: "If you place the pointer on a small residential street,  the G-III+ will put a name on the street *most of the time* without having to zoom in to see it.  (The GM-100 does not have this ability)."

Ability of GM100 to display the "missing" street names without having to point is not clearly indicated. Let's zoom in and see the magic...

GM100   GIII+




Now, that's what I call the highest detail available for GM100



Also J&J mention that both units use Tiger maps, but that the G-III+ has more updated maps, apparently equivalent to Delorme's Street Atlas version 5.0.We have checked out the GM100 maps against Delorme's SA version 3.0 and it clearly has more and newer roads displayed, so from that I can conclude that the GM100 maps are at least equivalent to SA version 4.0.

3)      Garmin Map Source has a noticeably higher shoreline vector resolution than the Lowrance MapCreate.

J&J demonstrate this by using three pairs of comparison screen shots of the Lake Lanier area.In our opinion there is not a great deal of enhanced shoreline vector resolution in these maps, even though they are displayed at nearly the maximum zoom level for both units.It certainly doesn't appear enough to be of any functional advantage, even at these high zoom levels.Once again Lowrance has eliminated a few minor details, while significantly increasing map memory availability.This is an advantage for the GM100 in our opinion.


Part 2 -- Comparisons That Were NOT Made:

Here are some of the features that we felt were important, that were not compared directly in the text of J&J's review.As we see it, there are 4 MAJOR advantages (#1-4 below) of the GM100 over the G-III+ and several other important ones that need to be addressed.

1)   Method of selecting map areas to be uploaded

As J&J point out, in the G-III+ system the smallest area that can be uploaded is the size of a county.In some states, counties can be quite large, thus not allowing much versatility in the area selected.The GM 100, on the other hand, allows the user to select areas for upload by a grid system.The grids measure about 12 miles on a side, which translates to an area of about a 144 square miles per grid.The average sized county in the Maryland area, at least, is made up of anywhere from 3 to 6 grids.The smaller sized grids allow much more flexibility in selecting the shape of the area to be uploaded.† By connecting the grid points either horizontally or vertically, any shape that you can draw can be uploaded to the GM 100, including narrow corridors along a route.

Here is a practical example of this advantage. Recently a G-III+ user was complaining in a thread on the sci.geo.satellite-nav newsgroup, that he could not upload the whole Chesapeake Bay area into his G-III+. The reason given was because of the fact that the G-III+ must upload by counties, and that Baltimore County alone took up nearly 1/4 of the memory. By using the grid system of the GM100, we were able to create a map that included the entire Chesapeake Bay from Norfolk to the MD/Pennsylvania line, by using only 1.30 MB of map memory. The G-III+ actually has enough memory (1.4 MB) to hold a map of this size, but its inflexible system of uploading by counties will not permit it to create a map of this shape.

2)      Method of selecting the map features to be uploaded:

The GM 100 allows the user to select only those map features such as Rural Roads, Railroads, Marine NavAids, etc., that will be needed for a given area before they are uploaded.This system prevents clogging up valuable memory with unnecessary map details, thus freeing up more memory to allow a larger area to be uploaded.With the G-III+, all map features must be uploaded.Unneeded features may be turned off after upload, but they are still occupying memory.

To further illustrate this feature, let's look again at the Chesapeake Bay map example above. We went back to the same map that used up 1.30 MB of memory and removed all of the highway and roads/streets data, leaving only the features that a person operating a boat might want, such as Water Bodies, Wrecks & Obstructions, Marine NavAids, Water Names, and Streams. The resulting map used up only 0.36 MB of memory! To carry this to its logical conclusion, we created a map, with the same nautical features listed above, of the ENTIRE EAST COAST of the United States (from Maine to Florida) out to at least 12 miles off shore. The finished map only used 1.89 MB of memory!

3)      Ability to upload 2 distinctly different maps:

Uploadable memory of the GM 100 is divided into two, 1 megabyte each partitions. It allows the user to upload 1 large map or two smaller maps. Combined with the flexibility of feature selection for each of the maps, it allows user to combine distinctly different levels of coverage. For example, on a cross-country drive or flight, increased road detail could be loaded for the entire route and additional street level detail only for selected cities.

4)      Ability to edit, create, and upload additional map details:

By using OziExplorer Mapping Software in concert with the OziMapCreate program, it is possible to increase the map detail and features displayed on the GM100.This will cost about $100 US, but it will do some neat things plus the OziExplorer Mapping Software is widely considered to be the best on the sci.geo.satellite-nav newsgroup.† See some of Andrew's handiwork with OziMC in the WORLD MAPS Section below.† † This feature represents a powerful tool that is currently available only for the GM100.This was mentioned briefly in passing in J&J's review, but we felt it deserved a great deal more attention.

5)      No audio alarm on G-III+

This is stated in the text of J&J's review, but they fail to mention that the GM100 does have an audible alarm.This is buried in a long list of features on their side by side comparison page, but we feel it is a significant advantage for the GM100. In our opinion, an alarm that cannot be heard is of limited value.

6)      Waypoint Management Software comes with GM100

The GM100 comes bundled with Lowrance's GDM (GPS Data Manager) Software.This program allows the user to create routes, upload/download waypoints, routes, and trails, and to work with MapSelect maps.This eliminates the need for 3rd party software that must be used to accomplish these tasks with the G-III+.

7)      Nautical NavAids Maps Superiority on GM100

J&J show 3 pairs of comparison screen shots that graphically demonstrate the GM100's superiority in NavAids maps, yet they only mention it briefly in the text.We feel that there is such a huge difference between the map quality here that it should make anyone needing a GPS for boat use to strongly consider the GM100.

8)      Ability to split the display into 2 different maps

Any one of 10 Group screens of the GM100 can be easily programmed to display 2 different maps (with different scales, orientations, detail levels etc) simultaneously on the screen.It is also possible to display your position in two different coordinate systems simultaneously with the GM100.Neither of these things can be accomplished with the G-III+.In fact, the GM100ís Group screens can be programmed to display virtually any desired combination of information.



There is no question that Garmin's Map Source delivers, for some areas, more detailed world maps than Map Create or City Streets do. However, none of them delivers enough detail or accuracy for anything, but very rough orientation. The only answer, we know,  to that problem is... make your own via OziMC.

The† screen shot of Madrid, titled OziMC, is a result of Andrew's 5 minutes on the web to find the info and another 5 minutes in OziMC to convert it to a map which he could upload to GM100. Currently there is no possibility of making real custom maps for G3+. Even though it is not an option created by Lowrance, we feel that it's of utmost importance to users around the world, therefore the "WORLD MAPS" section is the proper place to bring it up.

(Madrid Area)

G3+    GM100    (GM100) OziMC

Much better map of Madrid by Carlos Puch


Burlington, ON  CANADA

G3+  GM100 

(GM100) OziMC

It appears that G3+ has more railroads and place names, but lacks some of the water features the GM100 has. As for the OziMC enhanced GM100 maps, you be the judge...

If you are interested in finding more about OziMC, go to the "Software Reviews" section of this website or directly to the OziMC review.


Off to the NavAids we go...

For detailed information about what's included and what's not on MapCreate and City Streets CDs, go to LEI NavAvids

Another item of definite interest to mariners is the ability of GM100 to display reverse video - show land as gray filled. As shown in Florida area shots, the NavAids show additional info if you place cursor close to them. The Niagara River shot includes a wreck and an obstruction.


Niagara River

Chesapeake Bay

Also, check the Ship's locker for our review of the ECharts - Lowrance uploadable, Navionics, electronic charts.


All the screen shots on this page were obtained by various parties using G7TO

We'd like to extend our appreciation to Richard Bollar who provided Andrew with screen shots of Canadian Locations and other G3+ information. For LOTS more of G3+ screen shots with Richard's commentary see http://www.bollar.org/garmin.htm

To stay here, just follow one of the links below.

GM100 vs. G3+ Side by sideHome Earthmate StreetPilot III G3+ vs GM100 iFinder Lowrance DGPS EA3 Antenna Magellan 315 Review Magellan Map 330 Magellan Map410 review PhilSherrod Rand McNally GPS Infiniti QX4 SUV GPS