Maps are a little different now. For settings you have Starting Sector Size and Number of Sectors, the two are rather self-explanatory.

Think of a sector like a GalCiv3 map. One maps with multiple sectors you can travel between them via subspace streams.

To replicate a large map like in GC3 simply set Starting Sector Size to max and Number of Sectors to one.

Make sure to keep an eye on Recommended System so your system can handle the map.

thanks for the replies. And what if i set both sarting sector size and number of sectors to the maximum, will that be the biggest map?

I made the mistake of not believing them about the overall larger maps...for my first game. Some 59 colonies and close to a thousand unexplored worlds later (and about 3 days playing...) I was humbled. I have to cheer for Stardock in proving me oh so totally wrong.