For northern tiles, this is discussed by Trium in Merging 2x2's, terrain graphics (and random walkers). I used this technique for 2x2 tents on non-fertile ground in Palace Peaks. I think it would be difficult or impossible to recognize merging tiles when fertile or in central or desert maps.
The test map linked in that thread helps identify the tiles graphics. it's annoying but not impossible.
there are 8 tile designs plus their 'inverted' designs for each climate. 3 (6) out of those being the northern tile of the 2x2 houses will merge, so you can train your eye a bit to recognize those in each map. I actually find the northern tiles harder to spot than desert, with central being the easiest. they are specially hard to spot when they are covered by the fertile grass thingy.
Also, it's easier to spot the differences if the game is running in 4:3 resolution or with the widescreen or julius mods and not being stretched into a widescreen resolution.
Also, this is just a simplification of what is explained in a lot more detail in that thread but it's a more direct answer to what you're asking[This message has been edited by rFontana (edited 02-14-2021 @ 09:20 PM).]