Diffuse tiles
A tile is a landscape texture of 128 or 256 pixels. Diffuse tiles must have identical pixels on the left/right columns and top/bottom row, which will be drawn in game as a single pixel column and row respectively; this is necessary for proper texture interpolation.
Here is an image showing the pixels that will be overlapped, the left side is 256x256, the right is 128x128.
In the engine the red lines will overlap on each other, as well as the blue lines and in game it will look like the below example.
256x256 diffuse textures are broken down into 128x128 images and overlapped in the same way, as such the internal is also layered on top of each other like so.