Many (but not all) fiction authors are known for creating elaborate files of characters, plotlines, scenes, and of course, maps of the world or town or place where the story takes place. But if you have thousands or even millions of people reading your work, someone will find the inconsistencies in the carefully crafted milieus. I think it was fantasy author Piers Anthony who in the intros to his series books used to tip his hat to some of the readers who had written into him to flag the bugs.
Having tried my hand at writing quest-based far future fantasy (unpublished), I can say that for me the map starts out first in my head and then migrates to paper where it undergoes many revisions as the writing progresses. It didn't seem super hard, and because I wasn't super precise about distance covered I think there is a lot of flexibility. I noticed that George RR Martin's map in the "Game of Thrones" world can also be vague - other than the wall, distances between places aren't really articulated and it often seems that the distance from north to south of the realm when described in as people travel around is roughly equidistant to east to west, even though on the map Winterfell to King's landing looks to be so far apart. And, I might add, the lack of a map for the cities and other places across the sea is maddening - I just have no frame of reference for the location of the Dothraki Sea in relationship to Braavos, Valyria, etc.