Recently, in the course of attempting to assist another member who has an identical unit to mine (US purchased Nuvi 1300, with modded splash to enable LA, JCV & SLI) i had reason to examine my own Inventory to compare it with his.

From the hidden Diagnostics Menu of my 1300 US:

Inventory

Boot BLK B0972-00 5.80 nuvi 1300 Boot Black Software Pass
X-Loader B0972-00 5.80 nuvi 1300 X-Loader Software Pass
System B0972-00 5.80 nuvi 1300 System Software Pass
Basemap ?????-?? 0.00 Worldwide Autoroute Basemap 6FC01800
Suppmap Erased
Suppmap1 Erased
PROM 1 D0783-13 20.12 CN North America NT2012.20 LBD9A8300
PROM 2 Erased
Dlr DB Erased
Unknown D1074-00 9.00 Time Zone Map 9.00 03CBC600
JCV D3153-03 2.00 Junction View (JCV) 91A81917
Splash D1340-50 2.00 nuvi narrow+wide,TTS,TRF,LA,JPass
Demo Erased
FTL D0398-00 2.10 FTL Image
Audio D0376-00 2.00 English_Australian_Karen 73980200
Rmt SW B0360-00 3.30 MSN Direct Software 0535D7CA
Rmt SW B0901-00 2.90 GMT3G RDS-TMC Receiver 00440300
GTM20 B0482-01 5.50 GMT25 RDS-TMC Receiver 003F5C00
OEM Cnfq 0.00 Consumer default

I was struck by the inclusion of 'Suppmap1' as well as 'Suppmap' in the Inventory. i know 'Suppmap' is for 'gmapsupp.img' in SD/Garmin and i thought 'Suppmap1' may once have been reserved for gmapsupp.img in the unit itself, either in .system of 1xxx or in Garmin folder like in some other Garmin units. But of course Suppmap1 isn't reserved for gmapsupp in the unit's Garmin folder, 'coz no maps of any name will work there in 1xxx nuvis. And neither of those names will work in the .system folder of 1xxx series, the only recognised names being gmapprom.img, gmapprom1.img and gmapoem.img. The later may or may not be deselectable as i had heard and later confirmed.

In spite of this knowledge, i loaded a couple of small free maps (Rarotonga & Laos Cambodia Vietnam) into .system as gmapsupp.img & gmapsup2.img just for fun. Nothing changed, neither worked, not showing in Map/Info on the nuvi and Suppmap & Suppmap1 still showing as 'Erased' in the Inventory. As i expected, no surprise there. But why is 'Suppmap1' there in the Inventory anyway? Is it some over-looked hangover from some long-ago software predecessor of the 1xxx line? In the SD/Garmin folder, the little Rarotonga map as 'gmapsupp.img' showed up of course as 'Suppmap' in the inventory:
Basemap ?????-?? 0.00 Worldwide Autoroute Basemap 6FC01800
Suppmap ?????-?? 0.00 Rarotonga 0.00 006CFBB1
suppmap1 Erased
PROM 1 D0783-13 20.12 CN North America NT2012.20 LBD9A8300
PROM 2 Erased
Dlr DB Erased

When i renamed the little free maps as 'gmapoem.img & gmapprom1.img' in .system, as expected they worked and Laos etc as gmapoem.img was selectable and this was the Inventory for the maps:
Basemap ?????-?? 0.00 Worldwide Autoroute Basemap 6FC01800
Suppmap Erased
suppmap1 Erased
PROM 1 D0783-13 20.12 CN North America NT2012.20 LBD9A8300
PROM 2 ?????-?? 0.00 Rarotonga 0.00 006CFBB1
Dlr DB ?????-?? 0.00 Laos Cambodia Vietnam 2010 R5D663279
Unknown D1074-00 9.00 Time Zone Map 9.00 03CBC600

When i reversed the naming, Raratonga as gmapoem.ing worked, but was not de-selectable as it did not appear in Map/Info, just a space showing at the top where it should be, and this was the map Inventory then:
Basemap ?????-?? 0.00 Worldwide Autoroute Basemap 6FC01800
Suppmap Erased
suppmap1 Erased
PROM 1 D0783-13 20.12 CN North America NT2012.20 LBD9A8300
PROM 2 ?????-?? 0.00 Laos Cambodia Vietnam 2010 R5D663279
Dlr DB ?????-?? 0.00 Rarotonga 0.00 006CFBB1
Unknown D1074-00 9.00 Time Zone Map 9.00 03CBC600

So what i had heard was confirmed, some maps are selectable as gmapoem.img and some are not. I've also heard that some maps won't work at all as gmapoem.img. Anyone know why?

OK, so who cares? Because we can stuff as many >4GB anyname images in the sd's Map folder as we like, right? So what if there may be some other naming convention possible for an extra map in the .system folder... who's gonna use it anyway.. not me. But WHY the Heck is 'Suppmap1' there????

I bet more than one of you knows the answer to both questions......