A 'file overlay' is a special terrain type that places on the terrain a pre-made feature from a file.
The settings for each overlay, which you can edit using the 'edit' button in the overlay manager utility, include:
FileName | The file-name of the terrain file to use. See the overlay manager page for file paths and supported file types. |
VertScale→MinVal | The minimum altitude for the overlay, in metres. Should almost always be 0. |
VertScale→MaxVal | The maximum altitude for the overlay, in metres. Should always be greater than 0. |
VertScale→ApplyScaling | If false, use the default file vertical scaling. If true, use the scaling set by VertScale→MinVal and VertScale→MinVal. |
Resize→Width | The desired width of the overlay, in pixels. |
Resize→Height | The desired height of the overlay, in pixels. |
Resize→DoResize | If false, the size of the overlay is the same as the file. If true, the overlay is re-sized to the dimensions specified by Resize→Width and Resize→Height. |