I've been meaning to get into learning my way around using GIS software, and I think its use is a worthwhile skill to build. For the time being, though, all I really have to use it for is various fictional worlds I've made to various degrees - and for some where I've wanted a nice, organized way to put together things like maps of various demographic features and distinctions GIS seems like it would be well-suited to that sort of task.

However - I'd really like to learn my way around on my own geography, rather than on others in which I've much less emotional investment. In trying to start at the beginning I've run into the problem that the various tutorials and information I've been able to find all just grab an available dataset from one source or another to use as the base for a map, and have very little discussion on how said basemap/dataset/etc was actually constructed. Since most GIS in general use is concerned with the real world, this is reasonable and not very surprising, but it's little consolation to me when the first step in what I'm trying to do typically seems to be a matter left for the experts.

I'm not so concerned about constructing the content for the data itself - that's a different problem not quite so specific to GIS software, and one I think as it stands I'm already decently-equipped to deal with. But I'm not yet familiar enough with GIS software of any kind to know how that data needs to be packaged. In other words - what's the appropriate approach to constructing, say, a base map of land and political borders like that often seen of Earth, such that it will be usable in GIS software (for the time being I'm using QGIS, if that makes a particular difference). The borders themselves I've already got, if not necessarily in a vectorized format or even necessarily a digital one (yet), but I'm not sure how they should be formatted to work with QGIS and I'm having trouble finding any information out there that makes any explicit statement on the subject. I'd like to avoid sitting down and tracing a whole lot of borders only to find out that however I've gone about it has made a result that won't be very useful - for a land and political borders map, for instance, would simply manually constructing a polygon featureset by tracing out predesigned borders segment by segment and n-gon by n-gon suffice, or is there something 'special' about even a basic basemap that would be left out by such a method? While I'm quite unlikely to be aiming (or be able) to match real-world data in terms of resolution and precision, I'd like what data I do create or generate to be usable in the same manner as I could the real thing (since I'd like to construct an initial base to learn QGIS on).

To sum up, I guess the question is - what all goes into the actual file one would import into QGIS or other GIS software as the base dataset to begin mapping other features relative to, and how do I go about producing such a file (or is it really, really the same as any other featureset such that I could just build it out by hand from a blank canvas in QGIS itself)? I've seen some of the excellent pointers and guides posted here by Hai-Etlik (both the more general tutorial and the custom CRS info), but in looking around here and elsewhere I haven't found anything that quite covers how to put the base data together when not starting from Earth or some other dataset that someone else has already put together in a georeferenced form.