In the first (incredibly long) novel I wrote, I crafted the world completely from the ground up. I know the history five hundred years into the past, how organizations formed, how the politics work, how the lands were farmed and cultivated, where civilization sprang up and why. It was a massive undertaking, especially when you consider that all of that is just backstory for me to know. It was also incredibly fun, but when I finished the 1,000+ pages, I decided I wanted to make the next book easier on myself, so I decided to write an urban fantasy.
I based the fantasy (Conventional Demon) in the city I live in. Madison goes to places I've been to. Of course, I've created a few new places in the city, but there's still the Jamba Juice on the corner that Madison goes to for her drinks, and there really are office buildings where Madison's job is located. Even the nursery she buys her plants from really exists. I didn't have to do anything to create the physical world (not counting all the fantasy elements), and that was decidedly nice after the first novel.
One of the unforeseen joys of writing a modern novel based in my hometown was finding new places that Madison would like. I met with a friend today at a new nursery/cafe, and she prefaced the meeting with, "I think Madison would really like this place." She was right. I think Madison would adore it. I did, and we have similar (though not the same) taste. Meandering around the place even gave me a fun story idea. What a wonderful surprise.