When developing this map I have assumed you know how to develop a map in Giants editor, know how to use the placeable system, generally know how to develop a map.
To adjust the size of the map, open the map in GE, select terrain and adjust units per pixel. 2 UPI is 16.3km - 3 UPI is 24.5km - 4 UPI is 32.8km. It is possible to go up in smaller increments to get different map sizes. a maximum of 11 upi is possible but it would be virtually unplayable in game.
I have included the visual script needed for giant's editor to recognise maps larger than 8km, you will need to add these to the giant's editor script folder before opening GE.
The following use base game models, but you will need to use my modded xmls to get my productions.
simmons580/alexander580 map, newfruits, main productions and pallets - Achimobil - Autoload Scripts, Thundr - Meat Production Scripts, thesnake - World Productions