Writing a novel is not necessarily a tidy process. I have paper and electronic notes stacked all over the place. Ideas don’t come in chronological order, but rather pop in at the most inconvenient times. Then they get captured quickly and later on turned into story fragments that eventually become chapters.
By now, almost the entire book is outlined, with a good level of detail. During this process, I frequently discover new developments that lead to changes in the already outlined parts. So it’s a process of going back and forth. Since it is a story with lots of locations, taking place in a limited and specified amount of time and with lots of schedules to consider, the outline becomes quite detailed. (Which also makes it an easy reference when I need to verify some little detail.)
About two thirds of the book exist as at least a first draft. Here too changes often happen to the parts that are already written, to keep continuity.
In the actual writing process, I’ve pretty much started at the beginning and am working my way towards the ending. Although, the final chapter is already written, and there are some other skipped chapters that exist in outline, but for one reason or another didn’t get written yet.
Writer’s block hits us all at times and when that happens in one part of the story, I sometimes find that I do have the inspiration to move ahead with another part. That keeps the writing process moving forward, but does leave holes that I will have to go back and close later on.
In the end it is the steady process of writing on the story that keeps things moving forward. It’s a little like hanging out with a friend: the more time you spend together, the better you get to know each other.