..as has been mentioned above...
keep your original files safe in case you need to replace them.
I installed the scenery mesh for California in FS 2002.
Looks fine in places, but in others the default objects appeared incorrectly, ie:
Airfields were elevated or depressed into the ground!
Roads appeared up the side of mountains!
The sea appeared up the side of cliffs!
Buildings and trees floated in the air!
etc, etc...!
This was because of a conflict between the new scenery mesh elevation and the original positioning and elevation of the default objects...

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I have since reverted all my FS 2002 scenery and mesh back to the default settings...

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Try it out. It's fine if there are no conflicts...

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Cheers all...

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Paul.
P.S. It had no adverse effect on the frame-rates...

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Win 8.1 64-bit. DX11. Advent Tower. Intel i7-3770 3.9 GHz 8-core. 8 GB System RAM. AMD Radeon HD 7700 1GB RAM. DVD ROM. 2 Terra Byte SATA Hard Drive. Philips 17" LCD Monitor. Saitek Cyborg X Fly-5 Joystick. ...and a Briggs and Stratton Petrol Lawn Mower.