Ignore this post if your world is flat. Flat worlds are much easier to map.

Done properly, such maps would be in different projections so you can't just "zoom in" to a larger scale. Over a large area (small scale), you are going to have to pick a projection that fits the entire area which will be imperfect and lead to distortion. For a smaller area (large scale), you'll be able to fit the projection to that specific area much better to get a better map. The larger that the larger area is, the worse this becomes.

In terms of workflow, I'd focusing on the geometry of the features in the map, without worrying about presentation. I'd start with a rough idea of the layout at a small scale, then add details at the larger scale, and propagate the improvements back up to the small scale map. Once all that is done, then I'd do presentation. This is approximately how real cartography is done, except in real life we aren't just making up the data but rather have to survey, process, and analyse real world data.

Actually pulling this off without going all out and using real life GIS tools (Which means learning how to use those tools) varies in difficulty depending on exactly what you try to do and how you set up your workflow. Eventually it gets to the point where it's it's worth the time and effort to learn to do it properly with GIS. NASA make a free tool called "G.Projector" which can take maps in a Normal Equidistant Cylindrical projection, and project them to a number of other projections. Normal Equidistant Cylindrical is pretty useless for making a decent looking finished map but easy to convert to other projections. I think one of the other developers around here has a tool that can do transformations the other way without being too complicated but I don't remember who off the top of my head.

If you really want to go all out and try GIS, I've written an introduction to QuantumGIS in the tutorial subforum. http://www.cartographersguild.com/tu...using-gis.html