Indeed, it's very simple
Changes will be in this file :
XML/GameInfo/Civ4WorldInfo.xml
<iGridWidth>26</iGridWidth>
<iGridHeight>42</iGridHeight>
I think you know what you must change . Try to keep proportions!
It was just an advice, I never tested without keep proportions.You encourage me to keep the proportions, will that be a problem?
Are you guys building new maps for the RandR mod?
Whats the proportions (#x#) you plan for Gigantic ?
Let me know if they change.