How do I make very large maps? Which software should I use?

[tilt]

photoshop has a limit of 2 gigs (at least up til CS3 which I use) - I've hit that with my 16000 x 12000 map I'm currently working on, I'm getting around it by flattening stuff and saving as a new file. What are you going to use the maps for, if you're only going to print them on your own printer 200 dpi would be adequate, but if you plan to print professional then go for 300 instead.
Another option is using Illustrator or Inkscape which works in vector and therefor can be scaled up and down without loss/pixelation.
Personally I would work top down, its easier to make the whole continent and make that look good, then divide it up into countries after using the landscape to help decide where the borders go.

[Quabbe]

photoshop has a limit of 2 gigs (at least up til CS3 which I use)

You can safe your large files as .psb instead of .psd. That should be already included in CS3.

That way my largest file (12k x 12k px) with tons of layers had 5,xx gb.

[Razyda]

Hello,
This is my first training map.
Done mainly thanks to training on this site
Thanks all
Any feedback would be appreciated

[neelhtak_backwards]

Thank you for your suggestion of using .psb file formats. I had been previously working in a 8000x8000 odd pixel document with something close to 700 dpi. Although my computer is powerful, for some reason it just couldn't handle the psd file well - even though it was only 300 odd MB's. As soon as I saved it as a psb everything just loaded and worked far more efficiently. Thanks!