If you use software like photoshop or Gimp, then you have the capacity of expanding the size of the canvas. So you can start with, say a village and if your group move east, expand the canvas to the right and draw in what they find. It hadn't occurred to me before but this is a nice way to make a map that evolves with the direction the group moves in.
The downside is when the map starts getting a lot larger, the detail will be lost (and in fact will look like a mess) if you zoom out too far, but if you're thinking of printing your map on paper then because print resolution is much higher than screen resolution, it shouldn't be too much of a problem until your world gets really large.
My advice is that it can be done in this way, but you need to keep a close eye on resolution / point sizes for fonts etc.
The alternative is to have a map at a smaller scale for the macro stuff and make individual maps at a larger scale for the micro stuff.
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