1. Why are Leaks Bad?
2. Good Mapping Habit
3. Reasons for Leaks

Snapping to Grid

Like everything else in life, prevention is the key to leaks. Once you get a leak, it'll take a lot longer to find it and fix it. So how can you avoid getting them in the first place? Follow good mapping techniques is essential.

Taking your time when building your brushes, and making sure brushes are snapped properly to the grid can go a long way towards eliminating leaks before they occur. The cleaner and more organized you build your geometry, the more likely you are to be able to spot leaks when they occur, or even prevent them from happening in the first place.

You can also help prevent lots of extra work by compiling your level as you go along, instead of building your whole level before trying to compile it. Finding one leak at a time, while the map is only partially complete, is a lot easier and faster than finding a lot of leaks in a complete map that is full of geometry.

No Carving Please

One of the most basic functions a mapper must perform is the simple act of cutting up brushes. In particular, cutting holes in existing brushwork seems to confuse many novices. But before we go any further, commit this to memory: Never use the Carve Tool.

I don't know why Valve even bothered to create this tool in the first place, because using it is simply asking for trouble. All experienced mappers will repeat this mantra to new mappers over and over again, mostly because they had suffered the painful consequences of using the carving tool in the past. So listen to us and learn from our mistakes. Don't touch it; don't ever click on it; don't even think about it.

Why? Should you ask. Well, it inevitably creates messy geometry in the resulting brushes. It's known to split a perfectly-looking brush into hundreds of little fragments (okay, I may be exaggerating a bit here). But every sloppily made doorway or window becomes a future headache as you refine and polish your creation. Unless you learn to do it properly every time (i.e. not using the Carve Tool), you will always be limited to simplistic maps. In addition, carving will often mess up texture alignment, on top of creating unnecessarily complex geometry.

It also takes the compiler and the engine a lot longer to calculate and render these messed up geometry, and sometimes the compiler would simply give up. The only solution to this mess is to delete your map and start over. No mapper likes that idea very much.

And finally, if you attempt to use one of those messy geometry to seal your map, you'll most likely encounter leaks. And fixing those type of leaks is possibly worse than getting a root canal without any pain killer. Kids, don't try it at home.