Caution: only tested with
MSFS 2002 and 2004

Tips: General

How to install addon mesh.
Several alternatives are possible, but some offer more flexibility and control.
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Mesh priority and Rendering.
Mesh data is handled quite differently from other scenery, in part because scenery is positioned on top of the mesh, and also because there are often many mesh files covering the same area.
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Quality mesh - some practical considerations and screenshots.
The simple truth about mesh is that "You get what you pay for". The problem is, few know enough about mesh - to make informed decisions or to offer helpful advice. So we end up trying to compare apples and oranges.
The major determinant of mesh quality is the resolution of the data used to create the mesh. I have constructed a series of screenshots showing an approach from the SE to the top of Mt Washington, New Hampshire, crossing over Tuckerman's Ravine. These include examples using all the popular source data resolutions readily available for the USA, as well as the default mesh. (10m, 30m, 100m (2 LODs), 1000m, and default)
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What the mesh "numbers" mean.
A detailed description of these terms and what they mean to you.
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Increase the detail revealed in your mesh
Increase the setting for TERRAIN_MAX_VERTEX_LEVEL in your .cfg file manually.
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Flatten bgl files Fix flashing grass/taxiways at some airports
Adjusting the airport elevation often fixes this problem. The toolkit can also be used to adjust lake elevations, ...
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1600x1200x32 Full screen Resolution
This option sometimes disappears from the Options.Settings.Display.Hardware menu. What can you do about it?
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Some practical issues
Enhanced terrain mesh files only provide more accurate elevation information. Many of the scenery elements in the simulator are at fixed locations and elevations. For example: roads, lakes, rivers, coastlines, and airports. These may no longer "fit" the improved terrain as well as they did the less accurate original data. Not much can be done to improve this situation at this time.
There is often a substantial difference in elevation along the border between high-resolution mesh areas and the surrounding default mesh. This can produce obvious "cliffs" along the borders between them. I know of no practical solution to this problem, at least not for large areas.
The display of this additional detail imposes greater demand on computer systems. Several visual phenomena can develop if the system cannot meet this demand. (The actual sequence of events is not as simple as implied above.) Fortunately, there are a number of approaches we can take to minimize some of these situations. FS2004 seems to have dealt with some of these issues; I haven't noticed any suspended trees so far!