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I have a Garmin Edge 800 software version 2.40 and GPS software version 2.86 (latest version of both). It has the City Navigator maps for North America on a micro SD card. Unfortunately, they do not include paved bike trails, which are sometimes included as part of my routes, so turn by turn will not popup when you're supposed to turn onto a trail from a street or turn off of the trail back onto the street. Someone recommended the OSM maps as they would have the paved trails and would allow the turn by turn to work.

A popular mapset seems to be the Lambertus set: The ReadMe file on that site indicates if you want the entire North American map to download the 4gb file, 4000MB-lon_-159.96_to_158.99.2012-04-01.gmapsupp.img. That's what I did.

These are the steps I took: 1. Bought a new 8gb micro SD card 2. Put it in the 800, turned it on, set the option to record to memory card, started and then stopped the timer. This built the file structure for the SD card. 3. I pulled out the memory card and put it in my Mac laptop, dropped the img file (above) on it in the Garmin folder, and ejected it. 4. Put the SD card back in the 800 and restarted it.

The 800 then indicated the map could not be authenticated. Googling revealed a forum post where someone mentioned the .gma file was what authenticated the map. Nothing in the Lambertus ReadMe file indicated anything about any additional files being needed.

As an experiment, I copied the City Navigator gmapsupp.img file, the unl file and the gma file from the original Garmin SD card, dropped them on the 8gb SD card, and loaded it into the 800. When it was restarted, it still reported the map was not authenticated. The original Garmin SD card still works correctly, however.

In a post on this forum (, one user mentions that the Garmin file system and firmware can't deal with map files larger than 2gb. If that's true, I don't understand why Lambertus created a 4gb mapset. Even if it is true, I don't understand why the Garmin-supplied files, when copied to a larger SD card, weren't recognized.

Does anyone have any suggestions on how to make the Lambertus 4gb mapset work on an Edge 800?

Thanks for any help you can give.

This question is marked "community wiki".

asked 08 May '12, 16:51

johneasley's gravatar image

accept rate: 0%

edited 08 May '12, 19:00

TheOddOne2's gravatar image


Did you rename it to "gmapsupp.img"? If so, maybe you can try with a 2000MB and see what happens?

(08 May '12, 19:00) TheOddOne2

OO2: Yes, I did rename it to gmapsupp.img but that didn't seem to matter. There is online documentation that the Edge 800 is capable of holding many different mapsets with different names; as long as they end with the .img extension, they'll work. However, the name didn't seem to matter.

And that doesn't explain the mystery about why the original, Garmin-supplied gmapsupp.img and companion files, when copied from the original Garmin micro SD card to the new SD card, also wasn't readable.

The 2000MB file would not include the entire US. Would prefer the full mapset.

(08 May '12, 19:27) johneasley

No it doesn't explain that, but I've seen people with troubles moving maps (authenticated) between devices. (I've never used anything but OSM, so I couldn't say anything about it)

My eTrex can only handle "gmapsupp.img", while the Oregon can take anything with .img, I have no additional files (unl, gma)

I can understand that you prefer the full mapset, but as a test it can reveal wether it's a size issue.

(08 May '12, 19:45) TheOddOne2

Valid point about the size issue... one which I will test when I get home this evening and report the results here.

(08 May '12, 19:48) johneasley

Well, some progress. Sort of. I downloaded a 1GB mapset from the Lambertus collection, renamed it to gmapsupp.img, dropped it on the 8GB SD card, and popped that into the Edge 800. It still gave me the Cannot Authenticate Maps error message but it did allow me to see and enable the map in the setup. Even after enabling the mapset and restarting, it still did not authenticate the map. It looks like 2GB is, indeed, one issue but there is the authentication issue, too. I really didn't think it would be this hard.

(09 May '12, 00:39) johneasley

As a test I downloaded the 500MB-lon_-77.26_to_158.99.2012-04-01.gmapsupp.img from Lambertus, copied it to the Oregon, it worked for me. You could, as a test, also move that into the original SD-card and see if it works.

BTW, how's the Directory structure on the 8gb card?

(09 May '12, 18:19) TheOddOne2

Many of the folders found on the Garmin are also found on the 8gb card. One of the instructions to make this work was to set the Garmin to Record to Memory Card. This causes it to format the card and set up the folder structure. After that, you can leave the Garmin set as is or revert to recording to the internal folders.

There must be something different about the OS in the Oregon as compared to the Edge 800. I was hoping someone with an Edge 800 that had made OSM maps work would weigh in.

(09 May '12, 18:24) johneasley

From memory I think that one of the guys on the mkgmap mailing list has an Edge (might not be an 800 though). Maybe ask there?

(10 May '12, 01:31) SomeoneElse ♦

Thanks. I'll take a look.

(10 May '12, 01:39) johneasley
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question asked: 08 May '12, 16:51

question was seen: 13,366 times

last updated: 10 May '12, 01:39

NOTICE: is no longer in use from 1st March 2024. Please use the OpenStreetMap Community Forum