Thx flagmax. But like i said i didn't know what the heck i was doing in hex with the region number and just 'lucked-in' with the change for the Pacific basemap using 03 for 3 being that 1-9 in decimal is the same in hexidecimal. Woohoo!

So by thinking that the regions in hex were the actual regions numbers [how could they be, when there's 255 regions in a nuvi nv, duh!] i stupidly flashed that little gmapprom to rgn73 when i set the region# as 49 in the hex editor .... Brrr! Hope it's unused or my half-stuffed 2720 will be dead as a dodo if it tries to read from 73 at some point. The good news is that i've managed to clear whatever was stopping the secondary map gmapsupp working. I sent 'C:\Garmin\Sendmap20.exe -e' several times and now the secondary map works after it's loaded. Strange it couldn't be erased using the 'Erase maps in GPS' button on sendmap's GUI nor be overwitten before.

Further emboldened after your enlightenment i've made Ratatonga as an RGN using makergn.exe and the command 'makergn.exe gmapprom.rgn 49 gmapprom.bin'. I've not even an iota of an idea how the naming of the bin and/or resultant rgn files affects the naming of the primary map img written to rgn49, but i know that it has to be gmapprom.img in there so better to be sure than sorry. I didn't want to end up with some other img name and cause more problems. I know i said i don't expect you blokes to give me hex lessons, but if you know under what name the img would be stored if the rgn file is named, say, output49.rgn i'd like to know. Maybe it's somehow magically changed to gmapprom.img anyway regardless but if it gets stored as output49.img then it's not only unreadable it's worse than useless 'coz maybe it can't be overwitten by a correct gmapprom.

So just as a test, i then made my little map into an RGN using gmapprom.bin in RGN_Tool, changed the region# in hex from the default 33 to 31 and saved it. The two images files are identical in hash and hex compare. I then used Updater.exe to flash the file to the SP and bingo, i have Raratonga as the primary map.

Found another tiny map Norfolk Isl which i know for sure works as gmapoem.img in nuvi units. Changed the command line for makergn.exe to '50' and made a gmapoem.rgn and flashed it. Now have Norfolk Island in the unit's list of Detail Maps and it can be enabled/disabled [explanation for other readers: not all img files named as gmapoem appear in the list and/or are selectable even though they might work, depends on the map and some types won't work with that naming].

So this can potentially be used for some curing of these old units. Certainly corrupt maps in regions 3, 49 & 50 can be over-flashed using updater.exe. Also voices, pois etc can be overwritten with 'good' versions if we know where they're stored. In SP2610 i think that voices are stored in rgn17 [that's 11 in hexidecimal, see? i'm learning], maybe the same on SP2720 [if that's even right for 2610].

Importantly, does anyone know where gmapsupp.img is written to by MapSource/MapInstall/Sendmap20? I'm not game to use Updater.exe to flash a gmapsupp.rgn to rgn49 in case i break it. I'd like to keep this unit stumbling along for a while to play more with it. Maybe someone could look at the way sendmap20.exe deals with the image file to find where it's being flashed? I've done a [not case sensitive] search of both sendmap20.exe and MyMaps.exe in hex for region and rgn, and one for 'R' which drove me mad so many hits of course, the only likely result was an entry in MyMaps.exe of '3B' following '52 47 3E' which would be rgn59, but as it was in the list of supported files it's really only a semi-colon [;] in plain text i'm sure.

Are any of you software guys interested in doing some investigation on this stuff? Also looking if there's any possible way to dump regions with commands to look what's stored where ...... please? I'm prepared to offer up my 2720 as a sacrificial lamb for tests.