Thanks for your reply, Boyd

I think I may have
just found a
(somewhat hacky feeling) solution - Though I'll answer your questions first and get to that, as you might have a better solution

I was initially using TypEdit to create my TYPs, however I've
just found TypViewer which has less limitations, and a more code-based approach. I was initially using cgpsmapper to "build" the maps, however unfortunately the author is no longer around to sell me a non-watermarked copy, and so I hunted around and came across mkgmap which is perfect for me - as a developer I can inspect and debug to understand how it's behaving, and modify/recompile at will.
By "simple maps", I mean DEAD SIMPLE. Certainly not as complex as yours

Most of these maps are a just single poly type, some are a single poly type and a single polyline type, and one is a single polyline type. The one I'm initially focusing on here is only a 12kb IMG - 7 (~12 hectare) polygons of a few rural properties and their boundaries. While the area covered spans about 1/4 of Queensland, there are only 14 items on the map. Other maps have a lot more polygons with a size of about 300kb, but behave perfectly other than the same issues as I'm mentioning here.
I was using the 0x4a and 0x4b tiles but I'm also no longer bothering with them as they didn't help one bit.
As BaseCamp appears to currently display the custom maps (albeit wierdly) without being installed to the system prior, I'm avoiding installing the maps to the system as this will add another layer of confusion where I feel I'm already so close -
it shouldn't be hard to accomplish what you want if you set everything up properly
- I'm sure I've just got something wrong, and my TYP is overriding the basemap in BaseCamp...
[edit] if I compile using the --gmapsupp option and NO TYP file at all, the basemap is fixed but I of course have no custom textures/lines.[end edit]
[another edit] Maps with only POI's and a custom TYP cause no problem on BaseCamp whatsoever. I can have as many custom POI's as I want, as long as I have "Show POI ZIP First" disabled (or I get 'ghosted' points at level 0) [end edit]Through all my trial and error, I've found that it seems to come down to TYP files and drawpriorities. I tried experimenting with all sorts of drawpriorities from 0 to 40 on my own maps, with no luck.
Anyway, here's the solution I've come to in the meantime:- Find basemap and TYP files in Basecamp's program folder
- Use GPSMapedit to find all polygons used in the basemap (only about 12)
- Add only the relevant polygons' drawpriorities from the BaseCamp TYP to my custom TYP
- Compile map using --gmapsupp option
After doing this, everything is looking fantastic in BaseCamp! I just don't reeaaaally like how it's achieved, as I'm sure I've got some kind of flag wrong in the IMG filesystem somewhere causing JUST the polygons to be overridden. As a developer I don't feel comfortable redefining things that I haven't overridden - I'd rather find the conflict (if that's the case) and fix my error.
If this is indeed the correct or only solution, this may be why some "premium" maps have a ridiculous number of semmingly unused drawpriorities - perhaps a standardised drawpriority set is required by Garmin to maintain compatibility with other mapsets and basemaps..
Would a custom TYP in your experience normally override BaseCamp's basemap TYP and drop the default drawpriorities? Is this expected behaviour?
Thanks again for your input and assistance!
