A level is a rectangular piece of the game world.
Terrains are measured in meters. Length and width may be 32, 64, 128 or 256m.
Grids are measured in tiles. Each tile represents a square of 5m side length. Maximum size of a grid is 64x64 tiles to a tier, up to 10 tiers can be stacked on top of each other.
One or more levels make up a map.
In the source folder of a mod, a level is represented by several files:
a .lvl file (content of the level)
a .rlv file (pathing information)
a .tga file (minimap)