I got into fantasy RPGs (D&D -- happy birthday! -- and Tunnels & Trolls) before it was really common for the books to have maps. As a result I really got into drawing my own. This probably led to me writing material for RPGs a few years later. In fact, I generally started an adventure by drawing a bunch of maps and writing the map keys.
I recently got back into writing RPG material, and my style has flip-flopped. I write a huge amount of material, often with just a text editor, and write maps last:
That's a player-aid map rather than a GM map, so I can afford to be sloppy! Schematics to plot out the rooms in the adventure are more rigorous but not picturesque:
Right now I'm working on two solitaire adventures. They both have appendices for using the settings in GMd adventures. This means creating two city maps, and three or four maps showing the levels of a run-down gladiatorial arena in a forlorn desert city. Hopefully I can make something publishable-quality; I'm planning on self-publishing these and the less art I have to buy, the better!