Prioritization

In order to avoid conflicts between different scenery packages, X-Plane prioritizes all of the scenery installed on a user's system.

Files in the X-Plane\Custom Scenery folder are of highest priority. Within this folder, packages are prioritized alphabetically.

X-Plane's default scenery takes lower priority than the custom scenery.

For instance, consider a user's system that looks like this:
 * X-Plane 9\
 * Custom Scenery\
 * Awesome Boston Scenery\
 * Earth nav data\
 * +40-080\
 * +42-071.dsf
 * +42-072.dsf
 * Boring Boston Scenery\
 * Earth nav data\
 * +40-080\
 * +42-071.dsf
 * +42-072.dsf
 * Global Scenery\
 * -global terrain-\
 * Earth nav data\
 * +40-070
 * +42-071.dsf
 * +42-072.dsf

When flying around Boston, X-Plane will first check the Custom Scenery folder. It will prioritize the two DSF files in "Awesome Boston Scenery" over those in "Boring Boston Scenery." It is likely that the two packages in the Custom Scenery folder contain overlay DSF tiles (rather than base meshes). If this is the case, then after loading the "Awesome Boston Scenery" overlays (and ignoring those from "Boring Boston Scenery"), X-Plane will load the stock base meshes from the "-global terrain-" folder and place them under the "Awesome Boston Scenery" overlays. Wherever there is a conflict between the two, though, X-Plane will choose the data from "Awesome Boston Scenery."