From David B. Coe, the nuts and bolts about how to build a new world and some interesting insights about how outlines work into that process.
I had information about all the major dukedoms, I had royal genealogies for several countries, I had historical timelines, detailed maps, deity pantheons, myths and legends that I wrote and posted on my website. I knew that world inside out. And I think that the books benefitted from that.
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I believe in the iceberg approach — as a writer, I want to know EVERYTHING about my world (or as close to everything as possible). There is no way to give all that information to readers without resorting to data dumps, so I don’t even try. But what winds up happening is that the small details I do give manage to convey the weight of all that unseen work. There is enough behind each descriptive passage, that the details manage to add depth, dimension, texture, etc. without detracting from narrative flow….
So, how much is “enough” and how much is too much? I have no idea. It’s different for every book. I began the worldbuilding process for the Forelands by reading Greek, Celtic, Norse, and even Basque mythology, and by thumbing through old European history textbooks, looking at royal blood lines and historical timelines, trying to get a feel for the ebb and flow of “real” history. (My history Ph.D. is in U.S. — not a lot of royalty here, so I was treading on less familiar ground.) Once I had looked through that stuff I began working on my own maps and histories etc. I intended to do even more than I did — I only did timelines and lines of kings for some countries; I had planned to do them all. But at some point I began to realize that, a) I had the important stuff for all the important settings; and b) I had reached a point where I didn’t think that the stuff I was coming up with would do me any good at all, even as deep, deep background.
Link to the rest at Science Fiction and Fantasy Novelists