I always start with characters. Once I have the characters, I know what sort of universe they'd best populate. With Mallory Bash, She was originally going to be a space-faring kid that fought weird aliens and her world was quite neon. As I added characters, though, the whole thing became more meaningful, so I put her on Earth in the fictional town of Moonblush Village.
I still wanted the series to be about discovery, so I wanted a space bigger than a town. I created an entire county for her to roam (Nightdrift), and physically mapped out Moonblush Village and the surrounding towns. Full color illustrations with street names, businesses, forests, lakes, rivers, caves, mountains, neighborhoods, districts--everything.
Now, whenever you see a place in the comic, that place is concrete and it has a specific place in the town. This is important for the series because Mallory documents everything, and when a viewer sees these places, they need to stay consistent. I want viewers to feel like they could be placed anywhere in Nightdrift County and know their way around--know how to get from place to place, as if it were a real county.