Is the very well known "altitude correction" .BGL, used by many scenery developers, which is required to prevent altitude problems with AI, if you have 3rd party addons that change the altitude of the default airport and, the only place which will always ensure it will always loaded before anything else, is in the Scenery\World\Scenery folder.
While it's possible it might still do the same function when installed outside the sim folder, perhaps using a proper explicit Layer number, in order to be sure that some other products/installers/utilities might alter the Layer number, making the fix ineffective, we decided to use the tried and tested method, and install it into the sim, as we always did with every version of the sim.
However, while this might look like it won't prevent the absolute "purity" of installing everything outside of the sim, keep in mind the main advantage of installing outside the sim, is that you wouldn't be required to reinstall the scenery even if you MANUALLY remove the sim folder after Uninstalling it. If you "JUST" Uninstall the whole sim, using the default Uninstaller, our file won't be removed, because it's NOT replacing a default file that came with the sim so, as long as you don't ALSO manually remove the remains of the previous P3D folder installation, you will still get the same ability to reinstall the sim without having to reinstall the scenery, which was the main point of installing everything outside the sim to begin with.
So, it's all fine, unless you Uninstall AND manually remove the P3D folder after uninstalling. If you do that, you'll have to reinstall the scenery, if only to restore THAT single .BGL
