Weight files named _weight are found inside the modded map file directories. These files are usually stored inside a data folder (e.g.,mods/myMap/maps/mapAS/data).

Now and then you may want to change the _weight files (ex: asphaltDirt01_weight.png) and change the resolution of painted texture layers for terrain etc. For Farming Simulator 25 and below, it’s recommended to use a software called GIMP https://www.gimp.org/ and not PaintNET. The reason for this has to do with grayscale values.

Inside GIMP the Export Image Dialogue will look like this:

For _weight.png files, you’ll need to select 8bpc GRAY, which means 8-bit grayscale. The compression level is set to 9, and you can put everything else to what is shown above.

Remember that for larger Farming Simulator maps, all _weight PNGs must be upscaled. For a so-called x16 map, the resolution for the terrain’s _weight texture layers needs to be precisely 8192 x 8192 pixels.

If not all _weight PNGs are upscaled or have the same size in pixels, GIANTS Editor will show an error like this one below:

Error: Terrain weight map 'C:/.../maps/mapAS/data/asphalt01_weight.png' size incorrect. Same size (8192px) for all layers is needed.

Reference: https://forum.giants-software.com/viewtopic.php?t=212169