HI,
I've recently finished the first Ultima Underworld and have just started the second.
I've found that after a certain number of entries on the map (I haven't counted it, but I can if it helps) that any extra entries seem to disappear when you close the map and reopen it again. I never encountered this problem on UU 1 and I was wondering if anyone else has run into this (and have overcome it).
I never played this game prior to GOG, so I have no experience with the original version(s) and I can't seem to find any relating issues across the internet. I have found some websites offering a patch for non-CD releases but the GOG release seems to be wrapped in an ISO and a little tricky to edit.

I appreciate any help/advice that can be offered.

The ISO can be edited with a bit of effort. I'm not familiar with the map mod you're talking about but it should work with this method as long as it ends up in where the game looks for it.

Thanks, Arkose. I was trying to find a way to manipulate the ISO, I just couldn't get my head around it.

I run into the same problem. This is very nasty because I'm writing a walkthrough about UW2 and I want the maps as detailed as possible. Did you solve this problem MrMcAwesome?

No, I'm afraid not. I believe (and this was about a year ago, I apologise for not updating this earlier) that in the end I found that (I think) each map would hold only a specific amount of entries (12, 13, etc) so I just prioritised what was most important and put as much info as possible into each entry. But what I can't remember is whether EACH map had a specific limit or whether the entire collection of maps (or maps in each sector) had a total limit.
I can see how it would be frustrating trying to write a walkthrough - if you're doing it as webpages, then I suppose you could screenshot the maps and then add the text on top (photoshop, fireworks, gimp, whatever your preference), afterwards. But if it''s going to be video, then that'll be an uphill battle.
In short, I found no solution and I'm not technically smart enough to tinker with the code (if possible..?)

Thank you for your answer, even you have no solutuion it is helpfull :-)

You can find the outline of my walkthrough here if you have an interest.

Edit: I think each single map has a specific limit.

I have encountered a related problem, both in UW1 and UW2. I like to add notes to the map that remind me to come back to that point later. After I have returned some time later in the game and did, what I intended to do, I would very much like to erase that note. Of course I used the eraser icon and the note did vanish, but when I close and reopen the map the note always reappears. How do I get rid of notes again?

This is strange, I never have had this problem. I'm able to erase notes in UW1 and UW2. Sorry, it seems I cannot help you.