I understand for level streaming when another, for example, static mesh appears depends on the position you are, how to do it in UDK for example with another landscape connected to another landscape?
The transition has to be performed in a artistic way i suppose. For example a tunnel that connects the 2 levels or a cave,mountain, 90 degree angles passages etc.(if that is what you are asking)
If you are streaming in large outdoor areas, you should make your world map have lots of mountains, valleys, and canyons. Then like @O_and_N said, while you’re walking down a tunnel (or a canyon), you can stream in the next level that’s around the next turn.
You can make one very large landscape in the editor so that it’s all connected. Then once it’s made, you can move different sections of it into different levels.
I get all your ideas thanks : ).