Open World Solution

I have come to the point where I need to build a huge Open World.

I wanted to know what the best method was to begin doing that.

Firstly, I created 3 terrains that were 2000 x 2000 and placed them next to eachother, however if I was to raise the height a bit on one, you could see under from the other terrain. I could easily paint height for the other side, but then that’s a lot of effort to do all along the 2000 length.

What should I do? Should I use a third-party program? I need to build a snow environment, desert environment, etc.

Purchase Stitchscape

Did you try searching before asking? Before Auntie Google readily gave me lots of answers to your question:

http://scrawkblog.com/2013/03/21/creating-seamless-terrian-tiles-in-unity/

http://forum.unity3d.com/threads/seamless-terrain-question.19516/