This may shed some light:

1. You need first to capture or edit coordinates of points to create a .bln text file. There is a tool called "blnmarker" able to create such a file by moving plane on map and clicking every position.

2. Convert the data file with the DOS tool called "bln2shp.exe", using flag FL or EX (for flatten or exclude). This will create 4 files with the following extensions:

XXX.xml
XXX.dbf
XXX.shp
XXX.shx

The dbf file may be edited in Excel to modify the GUID and get every edit in the area: flatten(Y/N) / maskmap (Y/N) / exclude_autogen (Y/N).

3. Compile with the DOS "shp2vec.exe" tool to create the final bgl file and add it to the scenery library.


With FSX you must do it with a song and dance while you rub your belly and chew gum and stand on one leg the entire time. It's by design and why they did that is a mystery to me other than the changes in FSX allow scenery to be altered with the mission builder so it is possible they had to change the way FSX handles such things to accommodate that feature.