Start with a global map and then isolate areas to work smaller. This is the method I used for me home campaign world of Auren. I strated with the Continent, and then 'zoom' into other areas to work smaller.
CC3 has a means of copying portions to a clipboard that can then be inserted into a new map. Alternately, I often save an image of the area I want to zoom into as a BMP, and then insert the BMP and trce over it to make my maps.