Actually to suprise you I wasn't going to mention landmass ratio! (unless you've expanded bit of map you cut - anyway crash doesn't sound right)

Don't know about ATW as don't have that yet (and have heard map structure is different) - but as you're now on RTW - did you mean crash happens when you select 'provincial_campaign_name' from Provincial map menu?

If so its likely to be problem with
provincial_campaign_name_regions_and_settlement_names.txt
in the data/text folder
provincial_campaign_name has to be exactly the same as the name of your provincial campaign folder in
data/text/world/maps/campaign

May possibly also be to do with something being wrong with that file (but can't remember if that gives same CTD)