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Image file format and optimal solution for Garmin map

Started by larshgf, April 13, 2012, 01:20:48 PM

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Hi everybody,

I have just purchased a Garmin eTrex30 and would like very much to load it with an image map of my favorite Greek Island Samos. I can scan a map but would like to know the best image fileformat and the best reslution for the Garmin.?
Also I would like an advice on how to "georeference" the scanned map?

Best Regards
Lars - newbie


There are several programs that will also help you go beyond the simple technique on Garmin's site, such as


Thank you both of you for the answers. Then websites and programs looks very interesting. I will dive further into the subject!

I conclude that JPG is the best file format and the solution might be as good as possíble and as the memory in the GPS allows.

Best regards


Not only is .jpg the best format, it's the only format that works with Garmin custom maps. The .jpgs's are combined into a .kmz file which is really just a .zip archive containing multiple images and an index file.

Now you could start off with any type of file you like though, such as a geoTIFF for example. But it will need to be converted into .jpg files before using in the .kmz. Each .jpg image can be no larger than 1024x1024 pixels, and you may have a maximum of 100 of these. This places some limits on how big a custom map you can make.


Quote from: Boyd on April 14, 2012, 06:24:09 AM
Now you could start off with any type of file you like though, such as a geoTIFF for example. But it will need to be converted into .jpg files before using in the .kmz.
GeoTIFF converted into a properly aligned jpeg could save a little work.  But the only way I know to do that is Global Mapper.  Did you have something else in mind, Boyd?


I also use Globalmapper. But I think some of the other programs for making Garmin custom maps can open GeoTIFF. According to the mapc2mapc homepage, it can do this using GDAL. G-raster seems to have a lot of capabilities too

QuoteG-Raster accepts four basic types of georeferenced raster imagery:

Type 1: Files with the geographic data embedded in the graphic file itself. These include:

GeoTiffs: TIFF images with embedded geodata
MRSID imagery (file extension .sid or .mrsid)
NOAA BSB imagery (file extension .kap)
ERDAS Imagine format (file extension .img

Type 2: JPG imagery ("Big JPEG") generated by the free program USAPhotoMaps. You will need to specify the UTM zone for the map you want to use.

Type 3: General graphic files with geodata in worldfile format for the UTM coordinate system (e.g. JPG with .jgw, BMP with .bpw, GIF with .gfw, TIF with .tfw). You will need to specify the UTM zone for the map, and also the datum and hemisphere if appropriate (default is northern hemisphere, WGS84 datum)

Type 4: General graphic files with geodata in worldfile format in any coordinate system. But you will have to: a) Know what that coordinate system is; b) Look up its EPSG code; c) Enter the code in the specified box

I haven't used g-raster but it looks like a very nice package, which is no surprise considering the author, who runs and is also a member here. I have tried mapc2mapc and it has one very cool feature. When you open an image it automatically breaks it into optimally sized tiles and displays them as a big grid. You can then turn each tile on/off by clicking on it. This allows you to maximize the use of your 100 tiles and create irregularly shaped maps instead of just one big rectangle.


Hi again,

I was earlier in this thread recommended these tools for my Garmin:

I have tried the first MAPc2MAPC with good results and it was possible for me with this tool to make a kmz file which worked well on my Gramin eTrex30.
Wil there be any additional benefit in using the second tool (G-Raster)??



I wasn't familiar with MapC2MapC so I just purchased G-raster the other day.  It looks like MapC2MapC has more features, but I'm really happy with G-raster as a KMZ generator all for the price of a McDonald's Happy Meal.  I'd download the free demo, and see if it adds any features you don't have.

If you become interested in creating vector maps there is an excellent tutorial available on this site, and an shorter one here.

Boyd, a registered version of G-raster will open a GeoPDF and save it as a GeoTIFF.  You can then open the GeoTIFF as a "USGS" quad and get a KMZ with the collar cropped off.  You can also set the KMZ to read above or below the graphics and set it to have 50% density when viewed in Google Earth.  The 50% density is handy when verifying alignment (which has been perfect) the few times I've tried it).

Considering all the GeoPDFs at the USGS Data Store it's an economic way to do what Global Mapper does.


Thank you.
- Wonder if Europe has something like your "USGS Data Store" ?


I have seen numerous reports from people in Europe who are envious of all the free publicly accessible GIS data we have here in the US. But do some searches on Google that include the name of your country/region along with terms like GIS, data, download, etc.

Indrid Cold

Quote from: larshgf on April 13, 2012, 01:20:48 PM
Hi everybody,

I have just purchased a Garmin eTrex30 and would like very much to load it with an image map of my favorite Greek Island Samos.
Will this work for you:


Darn, why didn't I think of that? >:( Lars, have you visited ? Those maps don't have topo, but should have pretty complete streets and POI.


Quote from: Seldom on May 08, 2012, 08:10:32 AM
Lars, have you visited ?

Not able to find But I have downloaded Samos from OpenStreetMap.
Is it correct that the OSM map type is a vectorized map?
It's possible to render this map. When doing this it is converted to a raster map?
Is it possible to say which type gives the highest quality of maps?



Quote from: larshgf on May 09, 2012, 12:11:38 PMNot able to find

I think that was a typo by Seldom :) - .gl should have been .nl - try this:

The maps at that URL will be in Garmin's vector format (.img files). Vector and raster maps serve different needs. Assuming that the data is accurate, vector maps don't degrade as you zoom in. If the author defines a line as 2 pixels wide, it will always be 2 pixels wide at every zoom setting and 9 point text will always appear as 9 points on the screen. This can be either good or bad, depending on what you want.

Raster maps are images, so if a line is created to be 2 pixels wide when the map is viewed with a zoom setting of 1 mile, then it will get fatter and "jaggier" when you zoom farther in. Same thing with text, it is scaled for one specific zoom setting.

But since they are just images, raster maps can be made from aerial photography or scanned paper maps. OSM maps are available in raster format as well - for a simple example, just go to The map you see is made up of PNG image "tiles" - you can right-click on the map and view the individual tiles in your browser, like this: