Hammer Source Map Construction Breakdown takes a look at what elements levels are made up of in Hammer Source. Knowing how a map is constructed inside Source helps you to understand your own process and what you need to do with your own maps.
The tutorial covers:
How the map constructed?
What elements are used?
How everything comes together in Hammer Source.
3 example map files were used from L4D2.
Brushes and Entities make up the map inside Source.
Brushes are the basic building blocks. Walls, buildings, skyboxes, roads are all made up of brushes. Brushes are best used to define the shell of your environment. Basic geometric shapes.
Brushes can also be converted into entities inside Hammer. When a brush becomes complex geometry it is often converted into func_detail.
Displacements/Terrain are also created from brushes.
Entites are various gameplay elements such as player starts, weapons. Entities are also lights, props (static, physics, dynamic), complex geometry and converted brushes.
When you are creating your environment, start with basic brushes. Simple geometric shapes.
Then move on to more complex brushes and entities.