Thanks - and I do see what you mean, that much of the relational analysis capabilities might go rather unused in a fantasy context (though I'd hesitate to say they'd be entirely useless - the reason I was interested in using GIS for fantasy maps is that for some settings I'd had a number of different metrics I'd wanted to put together choropleth or other thematic maps for over the same geography - it might be interesting to see if I could use that sort of analysis on a regional scale to try and put together better correlations between, say, concentrations of population ethnicities and proximities and which lingua franca/trade languages are dominant in what regions as a result).

Hai-Etlik actually did cover the projections bit to an extent which was pretty neat (they had a thread on here about how to define a non-Earth CRS) so I wouldn't say projections for a fantasy world (if of course drawn directly from real map projections) are necessarily off the table .

As regards my original question, I guess - then to confirm, just drawing around in QGIS itself is a fine way to create base vector data - regardless of said data's actual quality, it would be in principle usable as a base to reference other data with respect to? I guess my real confusion was that from the information I could find I couldn't really tell whether there was or wasn't any 'special sauce' of sorts to a base dataset, since nothing really talked about constructing one, just fetching them from elsewhere.