OK, Got the masking thing down, pretty easy.
Now here's my issue. the area I'm working in is that large area down South of that island, it has a large dome in the center, there is a road leading up to the dome and a parking spot. Just a little way up that road is an intersection with a light pole there, now, the road displays up to that intersection, but it don't show anywhere below that intersection to the south, everything to the North shows fine, but as soon as you pass that intersection heading to the dome, the road just vanishes, and even the SBX Road Vector don't show. Now I know FSX has a "boundary" for how far it will display things such as roads, I figured that out a long time ago, so I know how far out that boundary reaches, the roads I'm talking about are far from that boundary point, and they used to show, but suddenly they don't except at high altitudes, at GL, they don't show.
I've rolled back my video driver, but that had no effect, I've played around with the FSX sliders and none of them have any effect.
So why do the roads just vanish suddenly after that intersection, but above it, they show fine all the way to the exit.

What the heck is going on?
I can better interpret this anomalous display scenario when I have a ZIP of the current entire project file set.
I already had the "modified cfg" and didn't realize it, must have been put in when I installed either ADE or SBuilderX. But it's there.
AFAIK, only a 'normal' install procedure for SBuilderX (
not pre-configured), with a 'prompt' offering to install the "Modified Terrain.Cfg",
...or a manual install of both SBuilderX (
pre-configured by rhumbaflappy), and the "Modified Terrain.Cfg" from separately downloaded ZIPs,
...will actually result in one having the "
Modified Terrain.Cfg" installed in FSX.
Please confirm on your current installation of FSX, when viewed in NotePad (do
not edit and save !) :
[FSX install path]\
Terrain.Cfg
...contains
this entry at the top of the file:
"//------------------------------------------------------------------------
//This modified FS X terrain.cfg is the result of discussions among
// various scenery designers during testing of Flight Simulator X.
// The modifications are the work of
// Richard Ludowise and Luis F�liz-Tirado.
// November 2006
//------------------------------------------------------------------------
// Modifications include the following:
//
// - 3 new land class values added:
// 252-custom seasonal,
// 253-custom non-seasonal,
// 254-transparent
//
// - VTPLayerRenderPriorities
// changed 7=30000
// to 7=20000
//
// - all FS9 legacy shorelines 2-109 now have a GUID
// and a StripWidthMeters added,
// making them usable with Shp2Vec
//
// - wave effect removed from
// dry water body shorelines 10,28,37,64,100
//
// - wave effect added to
// lake urban perennial shoreline 41
//
// - legacy airport backgrounds (obsolete) 167-185
// changed FlattenMode=flat
// FlattenPriority=50000
// to FlattenMode=none
//
// - land class polygon white coral beach 192 now references
// coral texture, value 132
// instead of tansand, value 137
//
// - all default fs x hydro polygons 194-199 now reference
// non-rocky water, ocean_sea_large_lake_0
// instead of ocean_sea_large_lake, value 100
//
// - legacy water flatten and mesh-clinging water polygons 380-381
// now reference non-rocky water, ocean_sea_large_lake_0
// instead of ocean_sea_large_lake, value 100
//
// - added FS9-style land class polygons 383-385
// referencing
// 252-custom seasonal,
// 253-custom non-seasonal,
// 254-tranparent
//
// - added hydro polygon rockslope 386 that references
// rocky water, ocean_sea_large_lake, value 100
//
// - added wave effect without a shoreline texture, 387
//
// - added utility without grass corridor, 388
//
//------------------------------------------------------------------------"
My file Explorer is no longer showing file dates (that stupid update screwed it up, waiting for MS to fix it). I'll re-zip everything and link it to you, I keep forgetting about ADE Backup thingy. I've always used a "flatten Exclusion" under the roads to help remove vegetation from the roads, it's always worked with no issues, but that doesn't seem to be the problem. As stated above, the roads only vanish after that certain point. this is also happening in other areas of the project that also used to work fine, even after the move from the original location.
As I said earlier, I have an old "original" ad4 file set that "worked" with no issues, I loaded that file set up, and the problem still exists when it never did on that older file set, so something between when I started working on the PR scenery and the "old" version of the project is where the problem started. The old file set does not use the CXV road vectors or any modified terrain or GP-polys created with SBuilderX, it is just a standard AD4 project with no extras. That is why I kept that file set, just in case something went wrong, I could just go back and start over.
I can better interpret this anomalous display scenario when I have a ZIP of the current entire project file set.
I will be on the road again today, and shall look at this upon my return this evening.
GaryGB