When an author writes a story, they must create the world where their story exists. Saving the Land occurs on two ranches: the Double J Ranch and the Little River Ranch. They are in contemporary East Texas near a little town named Faith.
East Texas is real. You can research it on the Internet. But the little town of Faith and the two ranches are not. I created them specifically for Saving the Land. To bring them to life, I had to decide how big they were, how many buildings were on them, what type of buildings they were, when they built the buildings, who's family owned the ranches, etc., etc.
When we write, we are literally drawing pictures with words. So, it's not enough to know that there are three buildings on the Double J Ranch: the main ranch house, the barn, and the Foreman's Cottage. I have to know what they look like, how many rooms are in them, how are they laid out, which direction do they face. I collected pictures of old houses. I took field trips and wandered through houses built around the same time. Those ranches were so real to me, I could wander them in my thoughts. But that wasn't enough.
I finally drew a map. Drawing that map and calculating the distances between the ranches, the buildings, and the scene settings in the story helped me to understand many aspects of my story that I hadn't bothered to worry about before. Among other things, I realized that I needed to consider how far a quarter horse could realistically gallop without a rest as my main character raced to the climax of the story.
World building is vitally important. Not only for the author as they build their story and decide what is realistic and what isn't, but also for the reader. World building done well can allow an author to transport a reader into that fictional environment so deeply that they long to visit even after the book is finished.