Mapping a world: Start with regions, or start with the world?
Hope I'm posting this in the right place, please forgive a n00b if not.
I'm getting ready to start creating maps for a home-brew D&D setting, using some of the tutorials and resources on this site. (And, yes, I'll post my WIPs here for feedback and criticisms.) My immediate need is a regional map for the area the characters are currently hob-nobbing about, but eventually I will also need regional maps for other regions, as well as of course a world map so everyone can see how it all fits together.
For utmost fidelity, it seems like creating the region maps and then later piecing them together to form the world map would be the best approach. (Note that, at least for now, I'm talking about mapping the individual continents first, so the "seams" between them are just wide open ocean.) Using this approach, I can simply reduce the resolution of the individual continents, and the general shapes would still be recognizable between the world map and the region maps.
On the other hand, some of the techniques I've already seen in these tutorials seem like they'd do really well to take a world-map scaled region and blow it up to a realistic-looking regional map without destroying the general shape of coastlines and the like.
So, my question to people who've done this kind of thing before: What is the best way to make world maps and regional maps in such a way that they're clearly representing the same world?