Scenery System Frequently Asked Questions
From X-Plane Wiki
Mesh Questions
What is the Maximum Resolution of a Base Mesh
X-Plane does not have maximum resolutions; the file formats are variable resolution. Mesh resolution is limited by memory; you could support a very high resolution over a small area.
The current tools are limited to 90 meters horizontally and 1 meter vertically; these limitations could be removed or adjusted fairly easily in the tool source code, and may be improved in the future.
What is the Maximum Imager Resolution
X-Plane does not have a maximum image resolution; the scale of images is decided by the metadata files that go with terrain imagery. The constraining factors are memory (VRAM and virtual memory) and performance.
Individual texture images can be a maximum of 2048x2048 pixels, but you can use a theoretical limit of 32768 separate images for about 2-4 pixels per meter. In practice, system resource constraints kick in first.