You draw a grass tile. You draw a dirt tile. Then you try to put a dirt path on the grass and realize the two tiles do not meet: you also need every edge, every inner corner, every outer corner, the one-tile-wide path and the single island.
Counted properly, that is 47 tiles per terrain pair. Draw them by hand once and you will not want to do it for the second pair.
So I built a tool that generates the full set from the two source tiles: 47-Tile Terrain Autotile Maker. Free, no sign-up, and nothing is uploaded; it all runs in your browser.
Why 47 and not 256
A tile has 8 neighbors, so there are 256 possible neighbor combinations. Most of them cannot happen on a real map. A diagonal neighbor only matters when both adjacent sides are also connected; a tile that touches only its top-right corner has no visible corner to draw.
