Graphics Making map as whole or divided into pieces.


I'm making a platformer but my problem is that making little pixelart pieces fe: 20x20 not only makes creating map (for me) harder and longer but adding details is also a pain (because i can't see everything all at once until i place pieces in gamemaker). Like, can i just make map as a whole in graphics editor like 1920x1080 and make it into like 10 pieces of that size and not have to worry about optimisation? would that have huge impact on framerate? i know people like using grids and stuff it's just not really suitable for my workstyle and i hope i could make whole map at once in editor and not worry about anything.