An attempt to make a open world map.

I am attempting to make an multiplayer rpg (as in co-op 2 player)i have gotten the network script written, i have got a small little island for the characters to explore with monsters and all the loot you could imagine, but there is a problem with that, its small. ive attempted making a terrain that was 50000x50000(31.02 or so square miles) but as we know that ruined the terrain resolution making a detailed world almost impossible. so my next crazy scheme was to create 625 2000x2000 terrain squares and attempt to sow them together manually. sadly this brought the unity terrain editor to its knees and i was unable to edit detail cause the terrain editor kept going all crazy and flying all over the place. so my last idea is to keep the 25x25 2000 grid idea but make the land as an object in Maya 2011 any tips on this? how to paint it and apply trees since i cant use the terrain tools tree painter? Last but not least does any enlightened individual have a better solution than mine i would love to hear it! Thank You!

If I understand you correctly then you have made a terrain that you would like to keep, however it is too small and you would like to add further parts / expand the terrain. Instead of creating lots of smaller terrains around your first one y not just add one bigger terrain to your scene and place your first terrain onto that one… that shouldn’t slow down your editor and the player won’t know that part of the terrain is also under the island terrain, if that makes any sense. Hope you understood what I was trying to say xD