Making Advanced Outdoor Terrain while keeping your Poly-count LOW!
Tutorial:
I'm sure you have all played the map CTF-Conquest by the legendary Chris "Plutonic", gazed at it's beauty and then wondered how he got such amazing looking terrain. Well now you don't have to think or look no further, cause I have a way of doing it too and I'm going to share my technique of making terrain with you all while keeping the poly count lower than 30!
My technique is about 50 times better than using the "Floor Lofter" and even better than using terra edit. You can get the results you need at a fraction of the Poly count.
But wait, There's more.............no there's not, here's how it's done!
Using the 2d Shape Editor make a 2d shape that would look like a valley from a birds eye view. Make it huge!. While using the 2d editor for this Tutorial DO NOT move the green curser as it will f**k everything up.
(The picture below has been zoomed out twice. This should give you an Idea on how big to make it)

After this Simple task, save the 2d shape so you can load it
back up later. (This is Necessary!)
Extrude the shape with a depth of 768 and Subract it from your world. Open up the texture pack "Genearth.utx" and make the walls of your subtracted brush "Rock 7" texture and of a scale 4. Set you roof to "Fake Backdrop" and leave the floor how it is.
Now. Open up your 2d Editor and load the 2d shape you just made. You will notice it is made up of a number of triangles. Delete all but one of those triangles and you will get something looking like this. The picture below is the top triangle of the shape I made above.

Having the one triangle left and without moving the green
curser, extrude the triangle with a height of 128 and place it in align with the
subtracted brush like shown in the picture below.

Once this is done you need to do some vertex minipulation.
This is one of the hardest to do thing with Unreal editor because when not done
properly it will cause all sorts of nasty errors.
First turn on the "Grid" and turn on the "Vertex Snap" button. With this on the vertex's you move around will automatically join to another. With this done, by holding alt, move the upper middle vertex up a couple of units. (Avoid going higher than 8) NOTE: When moving vertex's up and down, make sure they are perfectly horizontally aligned in the "Top View", if this is not done correctly it will result in HOM and BSP cuts and holes.
Once the Vertex has been successfully moved vertically, it should look like this:

Once this has been acomplished, hit the "Add" button and add it to your world with the ground texture of your choice. Now open up the 2d Shape editor and load up the shape again. Delete all the triangles bar the one that connects to the one you just used.
(Confused????? Check the pic!)

After deleting them all, extrude it with 128 depth. Because you are using the same shape as you did with the last one, the triangle should line up perfectly with the previous one. (As long as you haven't moved the green curser, this will move it a few units left or right).
Now, the two top vertex's of the "Active brush" should be touching the two top ones of the added brush. (See pic below)

Beautiful, it's lined up.............but it's flat.....flats not real!!!! Lets make it real!

After doing this, you will have something looking a little like this! (I moved the vertex done in this case!)

Now, open up the 2d shape editor and delete all the triangles bar the necessary one (The one that touches the one you just used) and extrude to 128 depth. Now, you will notice that one of your vertex's do not line up with the Poly you last added, simply make the corrections by lowering or raising your vertex to the point where it "Latches" on to the right place. (it will only latch on to another vertex if "Vertex Snap on" is set). Now that every thing is lined up it should look like this.
. . . . . .. . . . . . . . . . . . . . . . . . . . . . 
See how it's all nicely lined up? Does it look real?? if not, just move the spare vertex up or down until it looks right!
After lining it up so it looks nice, "ADD" it, and go on to the next triangle, then the next......and then the next until you've done all 6 of them. Then go onto the texturing. When texturing avoid changing the scale to anything higher than 3 times bigger, it tends to look shitty. Use a variety of different shades and tones to make your outdoor area look nice. Then, once this is done, select all the surfaces and set them to "Bright Corners" under the effects, this will make it un shadowy and natural looking!
And the end result......
Only 100 Polys
Only 32 Polys!
Or this Beauty, only 113
Polys
Conclusion: So now you now how to make awesome looking, outdoor scenes. . . so get to it! be creative!
FINAL TIPS: Use alot of decorations in your outdoor scenes. Mainly the trees and plants. If you think the plants are to small, make them bigger!
Also, remember use the most realistic textures you can find, the best packages for this are "Genearth.utx" and "Genterra.utx". Also always have some water. makes everything look so much more natural. Get the lighting nice and the sounds going good to. And to make it even more spectacular, have a beautiful, no more than 15 polygonal moving skybox!
And finally, always check your polycount, remember, you want to keep the Polygons under 150 and the Nodes under 350. Have Fun!