Working with someone on a new map

Hi all , i am looking at making a map with my better half , iv’e worked on maps before namely terra nova with uzumi , but when i joined he already had it set up so the map was broken into sections and he used to just give me a section to work on and i would work on it save it then upload it to googledrive , my question is firtsly how do i split a map into sub sections , so far i have no more than a flat landscape , and secondly how would i go about working on it with my girlfriend , i know google drive is an option , is there anything built into theeditor that can allow you to cllaborate or is there another way of doing it thats more effective ?

Many thanks in advance