...import a handdrawn map into photoshop at the correct scale?

[Ascension]

Here's what I do to put a continent in it's own document:

1. Make sure that you are on the correct layer. Use Layer - Flatten Image if you want.
2. Use the Rectangular Marquee tool to drag out a rectangle around the continent.
3. Edit - Copy.
4. File - New (leave the settings alone, don't touch them).
5. Edit - Paste.
6. Image - Image Size = make sure that the box for "Constrain Proportions" is checked then where it says "Pixels" in a box, change that to percent and then type in a new number...just remember to use the same number for all continents.

If you do this with a full color terrain map then resizing will cause pixellation (blockiness) due to the re-sampling issues (there are a couple of tuts explaining that). Just resizing a continent outline won't pose too many problems, though, but if you want to do terrain over the resized continent then you have to redo the whole map and it won't be exactly the same as the world map. Of course you could do this all in a vector program (Illustrator or Inkscape) but you don't get the same bells and whistles.

My advice to you would be to put each continent into its own document, do up whatever terrain you want for each continent, when done then stitch them back together like a puzzle in a much larger document that will contain all continent maps, then do the ocean last so that it is seamless. Then you can cut the continent maps up again and put them back into the older continent map document as a "final layer" that you would save as jpg and post it up so we can all see it. I have attached some examples that I just doubled. Number 2 isn't showing correctly, but if you right click/open in new window it will show.