This tutorial is designed for intermediate to advanced map designers.
Many people want to know how to make realistic outdoor environments. The problem is that this is the wrong question. Every map made for Half-Life 2 is nothing more than a series of rooms and corridors that lead the player from one problem to overcome to the next. A good mapper will disguise this basic fact by clever design and interesting visuals. I will underline this There is no difference between a set of concrete corridors and an outdoor area at the most basic level.
With this in mind the correct question is thus. I have a route through my map that needs to look like its outside. The emphisis is on route first, visuals second. So without a further ado I will lead you through a step by step guid to create an interesting route through realistic looking cliffs.
Start with your basic room, four walls a roof and a ceiling, texture them in the sky texture with the exception of the floor which should be a covered in the nodraw texture.
Next in your mind or on paper decide what you need to achieve in this section and the direction of travel. The 'S' represents the start point and the 'E' is the end point. I want the player to make use of most of the space in this section and I need him to exit on a higher level (NOTE: It is easier to restrict a players movement on an ascent rather than on a decent as the player could simply jump off if they choose to).
With the route descided the next stage is to decide what the core componants of your map will be. these are the basic corridor walls that keep the player on track. The initial direction is from the top left to the bottom right so an L shape against the top right is required. The player also needs to travel higher point in the map so in the bottom left corner there needs to be a hill or mountain to climb, since I want it to be an obvious destination it needs to be higher than the containing L shaped wall so I will make it two teared, each level acting a step in the players ascent.
Now we have our basic building blocks down we need them to look like cliffs. First we need to make them displacements, since I want the cliff sides to be rough and angular looking I set the displacement at its lowest setting (2).
The top generealy is covered in grass or at least a fine top soil on most cliffs and so I want it to be smoother so I set the displacement resolution a little higher (3).
The next stage is to rough them up a bit, with all the sides selected (but not the tops) I then add a noise of a maximum 64 minimum 0 to them. And then neaten it up by using the Sew command.
Next I need to make the top more rounded and uneven so using the Terrain morph brush at its highest setting I push the surface up and down gently using a tapping action on the mouse key. Think of it as if you were a blacksmith gently beating out the shape of a bowl or something similar just lightly tapping it will give a more pleasing shape.
finally using the X axis and Y axis alteration I need to pull out the sides and push in the corners to give it a more rounded look. You may have realised I haven't used the subdivide command to achieve this, this is simply because it can destroy the shape of the walls and lead to a confusing layout. It has its place but not in cliff construction.
The finish cliff.
I repeat this process on all the cliffs until they are fairly irregular while still holding their basic shape.
You may have also noticed that I have altered the hight of the walls of the room containing the cliffs, you should be prepared to do the same, displacements are fluid in there construction and you should be prepared to giveway a little bit to accomidate them.
With the guiding walls in place I need to place the ground in next. When I refer to the ground I am refering to the lowest point of your outdoor section this generally manifests itself as one large brush covering the bottom of the room.
The ground needs to be made so the displacement on the top is flush with the nodraw base to make maximum use of the space.
This then can be tapped with the terrain morph brush to make it a little uneven, concentrating around the edges of the cliffs.
STEP 6 (RAMPS)
In order for the player to be able to reach the top I need to include a ramp for the player to reach each new level.
First I pull up the ground so it reaches the top of the next tear on my mountain using the morph tool at its largest setting and then I pull it up some more so it pokes out.
I then use the smooth tool to flaten it out and remove some of those sharp angles. by having the peak of this ramp slightly higher than the cliff edge it allows some leway as it is slowly flattened out.
This technique is repeated on the second level of the mountain so that it reaches the top, remebering to use the sew comand to tidy it up afterwards.
Thats more or less the basics of cliff construction and Outdoor environments within Half-Life 2, however there are a few 'tweaks' that can be done to make it better.
Sometimes when altering the hight of cliffs, especially when they are altered significantly like in my ramp the texture can become stretched and distorted.
This can be easily fixed by using the terrain morph tool at its smallest setting and raising and lowering the intermitent points on the displacement so they are more evenly spaced.
The great thing about displacements is that they can intersect each other with no problem unlike regular brushes. make use of this if there is a particularly long and boring section of cliff then you can break it up by inserting small blocks and turing them into cliffs so that they break up the continuaty. Alternatively they can be added to fill up a gap like in my map.
Follow these basic principles and hopefully you too should end up with something similar to, or even better than, this.