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Terrain Size FS17
Please forget that 2X, 4X etc terrain size nonsense, use kilometers (KM) which is "kilometers x kilometers" (in short just km) instead. Simple example; FS17 Goldcrest Valley is 2km, FS17 North West Texas is 4km, FS17 Broad Acres and FS17 Cornbelt are 8km. As of 2018-08-05 nobody has released 16km terrain. You can read more about using actual terrain size from Terrain Use Actual Size (FS19) tutorial page.
0,0 coordinates is upper left corner, max coords are lower right corner.
Terrain size is defined in map01.xml file using meters. Also you need a supporting MyTerrain\maps\map01\map01_dem.png heightmap image and the *_weight.png ground texture images, more specifically in their resolution to fit your chosen terrain size in meters.
map01_dem.png image pixel resolution, in-game coordinates, kilometers x kilometers size:
255 x 255 pixels.
513 x 513 pixels, 1535 x 1535.
1025 x 1025 pixels, 2048 x 2048, 2km x 2km (size of FS17 Goldscrest Valley and FS17 Sosnovka)
2049 x 2049 pixels, 4096 x 4096, 4km x 4km
4097 x 4097 pixels, 8192 x 8192, 8km x 8km
8193 x 8193 pixels, 16384 x 16384, 16km x 16km
16385 x 16385 pixels, 32768 x 32768, 32km x 32km
Obviously you cannot use 8193 x 8193 pixel resolution heightmap size not to mention 16384 resolution, it is way too large, all you would get is performance issue lag, unplayable FS17 state.
Configure your terrain size in meters from map01.xml config file, have fitting heightmap image for it. Easy 