So, I had a great idea for a post about world building, and then I read a great post by Claire Buss on the same topic (read it if you have a chance), so I don't want to rehash what Claire (and others) have said.
But, I do have a unique perspective on world building - in an English class "compare and contrast" required essay sort of way. I have two books coming out - Unremarkable is being released this month (in 7 days in fact!), and the second, Wrath of the Fury Blade comes out in April. Both are fun books, and each has its own share of world building, but each is quite different on how Coy and I approached them.
Unremarkable takes place in 1929 Chicago. As a historical setting I did a lot of research to get the feel and character of the city right. There is a lot of name dropping to locations, streets, and places in Chicago to help set the scene. In fact one reviewer pointed out that the book feels a bit unsure about the city. And I will admit that that is probably the case. (Edit: the reviewer did like the story, and does recommend it, but I take their comments to heart.) While we had some historical locations within the city to draw upon, the story is set in an alternate world where the supernatural (vampires and such) are real. While not open and known to all, they are there, so creating the mythology of the supernatural elements, and weaving it into the story was the fun (and challenging) part.
Wrath of the Fury Blade in contrast is a story set in a completely fictional fantasy setting. I am a huge fan of Ian Rankin and his Inspector Rebus novels, and in Rankin's stories the settings of Edinburgh and Scotland are an integral part of the story. We wanted our fantasy city to be the same way, so we spent a lot of time mapping the location. I even drew a map to make sure I knew where everything was located and made little marks all over it whenever I placed a building or event. But just having the locations wasn't enough. The city - called Tenyl - needed to be lived in, to feel like it was more than just stage dressing. We had to think about the language, the culture, the food, the magic, and everything else. We wanted there to be a history to the locations, and to have everyday objects to have meaning for the residents. In the US we Americans have all sorts of slang for our money - "bucks", "greenbacks" "Benjamins", "dough", etc. What about in a fictional fantasy world? Calling coins generic "copper pieces" or "gold" wouldn't cut it, So silver coins are called Marks by the treasury, but the locals use slang to refer to them, calling them "Skippers" or "Skips" because of an ancient legend about a silver coin being skipped across the river to found the city. It was this level of attention to our world building that helped get us a review that said "In this marriage of fantasy and procedural thriller, the team of Habiger and Kissee...gives fans of both genres a master class in worldbuilding."
So, where was I rambling toward? World building can have many different facets to it, whether you are building on a historic setting or starting from scratch. Both are necessary, but there are different ways of addressing each, and the level of detail necessary to make both worlds seem real may be different. In the end it comes down to the type of story and world you are trying to create.