GPSrChive Discussion Forum

So I already have an eTrex SE
I tested all possible variants and found that the GMAPBMAP.IMG file must definitely contain a map with the map ID "CITIES".
The CITIES map may contain:
Codes: 0x0100, 0x0200, 0x0300, 0x0400, 0x0500, 0x0600, 0x0700, 0x0800, 0x0900, 0x0a00, 0x0b00
Kind: Point
Category: Cities
The problem is that the standard map ID can contain only numbers and HEX codes and all sw checks this and won't allow letters to be used. Unfortunately, the "system" map from Garmin uses the letters in the map ID, in our case CITIES. I would need someone with high level knowledge of IMG files to help solve this problem.
Data from the second file F0071BLA.IMG eTrex SE cannot displayed. Maybe we'll see it in some future firmware, but that's just speculation. From my point of view, it makes no sense to deal with this.
I still see the CITIES mod as realistic. It would be good if each country could make its own CITIES.IMG file with all cities and villages, not just a few of the biggest cities.
In my opinion, the biggest shortcoming of the eTrex SE is the lack of POI support.

Did you try the ASCII coding for the map ID?
CITIES = 43 49 54 49 45 53 = 434954494553
F0071BLA = 46 30 30 37 31 42 4C 41 = 4630303731424C41

Not sure if you can add so many characters / such a big number.
Can even add a different one to try out. If it works, you can add custom layers to the map
OTHER = 4F 54 48 45 52 = 4F54484552
It's possible that the SW automatically converts from HEX to ASCII and shows text version of map ID, but when packing/creating a new map it expects "raw" HEX name.
Also possible that the GPS unit (eTrex SE) has a white-list of map IDs, and will not show any random name, just the ones in the list. So "OTHER" or "JOHN" will be ignored.

Worth a try, IMHO

No it doesn't work with ASCI, I used a hex editor to changed all the ID(which is encoded as ASCI in the Binary "soup") occurences, but it still doesn't work, also does the format of the map look a bit different.

I managed to edit the GMAPBMAP.img file from the eTrex SE!

Required SW:
* GPSMapEdit
* cGPSmapper
* GMapTool
* HxD (Hex Editor)

The Process:
I took the original GMAPBMAP.img file and used GMapTool to split it into two map files: 22906436.img (CITIES) and 22906439.img (F0071BLA). I opened the 22906436.img (CITIES) file in GPSMapEdit and imported my own POI database (in my case, a list of all 6,259 cities and municipalities in the Czech Republic). Subsequently, using GPSMapEdit and cGPSmapper, I compiled a new 22906436.img file. Then, I reassembled the files back together in GMapTool and adjusted the file header to this state:

Header: dd.mm.yyyy hh:mm:ss, DSKIMG, XOR 00, V 3.00, Ms 0, 006-F0071-00
Mapset: GMAPBMAP.img

Map size s-f CP prio PID FID Name
22906436 MPC 810172 3 1252 25 T 0 0 CITIES
F0071BLA MPC 77792 4 1252 0 T 0 0 Worldwide NR Small Basemap

Next, it was necessary to change the map ID from 22906436 to CITIES. No free map software is capable of doing this. This is where HxD comes in. Using a "hard" edit, I had to overwrite all occurrences of "22906436" with "CITIES". Note that it is crucial to maintain the 8-character length, so for "CITIES," you must add two spaces in hex code (20 20). The result looks like this:

Map velikost s-f CP prio PID FID Name
CITIES MPC 810172 3 1252 25 T 0 0 CITIES
F0071BLA MPC 77792 4 1252 0 T 0 0 Worldwide NR Small Basemap

This works, and the eTrex SE is able to display these points on the map!
I also tried adding other map elements to F0071BLA, but the eTrex SE was unable to display any of them.
The Conclusion:
We are able to add points/POIs to the map, but map elements like roads, contour lines, or rivers... not yet. At least not for now.

If you would like to see the modified Base Map file for the Czech Republic, containing all cities and municipalities in Czech Republic, the file is attached.

In the attachment I am attaching a modified file of the internal map in eTrex SE, the map contains all cities and towns in the Czech Republic, saved as POI points.
1) Back up the original file GMAPBMAP.img in eTrex SE (it is in the root directory of GARMIN)
2) Unzip the ZIP file into the GARMIN folder in eTrex SE, the original file GMAPBMAP.img will be renamed
3) And that's it

CZECH

V příloze přikládám upravený soubor interní mapy v eTrexu SE, mapa obsahuje všechny města a obce v České republice, uložené jako body POI.
1) Za zálohujte si originální soubor GMAPBMAP.img v eTrexu SE (je v kořenovím adresáři GARMIN)
2) ZIP soubor rozbalte do složky GARMIN v eTrexu SE, přemeže se originální soubor GMAPBMAP.img
3) A je to

Map File

GMAPBMAP_CZ.zip

Great find on how to make maps with custom POIs for eTrex SE.

I can confirm CZ map works on eTrex SE. Just a question - does it contain all of CZ or just part of it? As zoomed out view showed POI in "circle" area, rather than full CZ borders at first glance. Can you get idea from looking at this map where you are?

Yes, the map contains POIs (cities and villages) for the entire Czech Republic. The reason they appear in a circle rather than showing the whole country at once is due to a limit on the maximum number of POIs the eTrex can load simultaneously (approximately 100).
​This is also related to how points are loaded across different zoom levels, which I haven't been able to configure satisfactorily yet. Ideally, different sizes of cities should load at different zoom levels, but it isn't working perfectly.
​Yes, you can definitely figure out where you are even from such a simple map. It is quite usable from a scale of 5km downwards; the best clarity is achieved at scales of 1.2km, 800m, and 500m. It’s very effective for both hiking and cycling.