[Not a graphic glitch] But removed concrete is quite weird

[Ohz]

I feel you might want to know that after removing concrete, the ground tiles is pretty weird, destroying large patches of nice beautiful graphics. Feel free to delete my message if you think that's pointless.

[daniel34]

Related bug reports:
[0.12.20] Concrete and terrain conversion glitch [Bug Reports]
[0.12.2]biome borders keep refreshing border tiles [Not a bug]

The problem you are experiencing is caused by the tile-fixup logic. Basically, to avoid non-allowed tile combinations, like 1-tile wide water canal etc, the game fixes the tiles after any change. (This also chooses the 2X2 or 4X4 tiles to be used if the area is big enough).

The problem is, that you are changing tiles one by one, which is not only much slower, but also can do various results as the tile correction is done after every change.

The proper way is to save all the tiles you want to change into an array, and then do it by single call of the set_tiles method.

The solution given only applies to mods that do this in code, but putting down / removing concrete (with bots for example) calls this function one tile at a time and leads to this behavior.
The easiest way to demonstrate this is to lay down a concrete blueprint with bots over a small patch of a different biome and then remove it again. The resulting patch will look different (and repetitive).

[kovarex]

Did you see how the terrain looks when you remove a road or something?