i love everything ralph mcquarrie has done. for those who don't know, he did most of the star wars concept art, but he's also done his own pieces too. i have seen unreliable sources claim that this is an early bespin or coruscant concept, but take that with a pinch of salt

higher quality image, but cropped (and with the signature removed):

main image source || hq image source || ralph mcquarrie on wikipedia