MAPC2MAPC Help pages : Garmin IMG
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Garmin IMG maps are vector maps (made up of lines, points and areas) that can be used on Garmin GPS units.

An experimental extension to MAPC2MAPC will render these as 'slippy map' tiles either as OSM Tracker (z\x\y.png format) or RMAPS SQLITE format. There will usually be several zoom levels created spanning the range of 'bits per coordinate' specified in the IMG file.  The IMG format is very compact and the rendered file will be very much larger, even 100 times - depending on the level of detail. Rendering can take a long time, too, again depending on the map size and level of detail.

GARMIN locked maps will not be handled. You should also respect the authors' licences - some of which specify that the maps may not be reprocessed nor used on non-Garmin devices.

But I felt there are enough freely available maps to investigate what can be done so make these maps available on other devices such as Android and iPhone/iPad.

I have made some arbitary decisions on rendering rules but there is a parameter file that specifies colours and line styles of the rendered objects. I have created some Point of Interest icons, too.

I don't claim the maps are pretty but they are - as far as I can tell - greographically accurate.

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This is available without registration. Exit Wizard mode.

First, decide whether you want the output as sqlitedb or a standard z/x/y tile store and set that in the Garmin Tab of settings. Also whether you want to save space by using palette colour on the output map tiles : Settings Output tab : Reduce from 24 to 8 bits when saving (I recommend you use this even though it is slower)

Second, use utilities>Convert IMG to Mobile Atlas. If there are several IMG files then select and open them all at the same time.

There is an opportunity to reduce the area that is rendered and some other choices that you may want to experiment with depending on the device you are using (e.g with very fine pixels select oversize text) then leave it to process.

When the process finishes, you can use View to see the result - if you have made a sqlitedb then open that otherwise go to the _atlas folder and open one of the .png files.

Don't be surprised how much bigger the rendered map is - 10 times is not unusual!

I acknowledge the invaluable content on these two documents :

http://sourceforge.net/projects/garmin-img/files/IMG%20File%20Format/1.0/imgformat-1.0.pdf/download
http://pinns.co.uk/osm/docs/expl_img.pdf