It does not matter where you install the mesh on your system, nor what layer/priority is assigned in scenery.cfg, since the sim does not consider layers where mesh is concerned. We have no control over how mesh is used, other that to Activate/Deactivate it in the Scenery Library or remove it from the \scenery folder.

Mesh information from all "active" Scenery Library layers is "pooled";

    When the LOD values differ, the higher LOD level mesh file is used.
    When the LOD values are the same, the higher source data resolution mesh file is used.

FS2004 still uses the mesh file with the highest LOD. But we can no longer rely on mesh with the higher source resolution being used when the LOD is the same. This is a matter of some importance for both developers and users of add-on mesh data.

FS2004 rules for mesh with the same LOD:

Implications:

Test procedures used to confirm the above rules:

The software uses a few basic rules (version-specific, see above) to determine which data to use to construct the terrain as a series of concentric rings extending from the aircraft to the horizon, with less terrain detail rendered as you move toward the horizon.

* LOD determines the radius of the mesh actually displayed under the aircraft. (e.g. LOD12 mesh has a radius of only about 7 nm, LOD10 mesh extends 30-40nm)

* Beyond this radius, the "priority" of the mesh used under the aircraft drops to 0, and the rules are applied to determine which mesh data is used to render the terrain for the next concentric ring of mesh. The radius of that ring will be determined by the LOD of the mesh available for that region.

* This process is repeated until the horizon is reached.

The sim may always use the lowest (default) LOD world mesh at the horizon, or do something entirely different in FS2004, where distant mountain profiles seem to behave strangely.

Mesh constructed with an LOD of 12 or higher is not used at all with the default fs2002.cfg/fs9.cfg settings.

In FS2004, mesh constructed with an LOD of 10 or higher is rendered exactly the same. An LOD greater than 10 (38.2m) only increases the file size and reduces the radius where the mesh is rendered.

The above factors determine the maximum possible amount of detail rendered by the sim. Settings in the sim allow users to reduce the actual amount of detail, usually to improve performance elsewhere.