Difference between Structure and Detail is crucial

The most common error of people who start mapping ist the MAX_MAP_VISIBILITY! And its the worst what can happen to them! They map for months and they add more and more stuff to thier map... not knowing about the difference of stucture and detail. When they get the compile error it is often too late!!! Sometimes you can't just change thousands of brushes to detail.
One who has expierenced this with his first map is my mapping partner Dacrow. He has build a fantastic map... but when he was about 75% finished he has stated getting the vis error when compiling the map. The compiler just aborts the compile process at vis and light will be never compiled. He has even released a beta map that is showing how a map looks like when you don't know the difference between detail and structure. (download it here to see a map with average 50,000 r_speeds)

I have made a small example map to show you what needs to be stucture in a map and what detail.

Screenshot #1 - The map

Here we see a map like you would build. A simple room with some stuff in it like crates, lamps or tables.

Screenshot #2 - Decide what needs to be made Structure or Detail

A simple rule for making brushes Stucture or Detail:

• Walls and Skyboxes / Hull nedd to be Structure. Otherwise the map will leak and won't be compiled.
  
• Small brushes need to be Detail

On this screenshot all small brushes are highlighted. These brushes need to be Detail! To do so Select a brush and press the button Ctrl and M simultaniously (Ctrl+M)

Screenshot #3 - Check what has been made Detail

Press Ctrl+D like two or three times to check what is Detail and what is Structure. Notice that our room is like empty now. Only the Walls are Stucture... all other stuff that is Detail is not visible on the screenshot because we have pressed Ctrl+D once. You can switch Detail on/off by pressing Ctrl+D. The brushes are still there so don't panic ;) they are just hidden when you turn off Detail in the viewports.

Screenshot #4 - Another room

Another room... just to show what else should be made Detail. On the screenshot we see an alpha texture with missleclip on the bottom side. All this stuff needs to be made detail. Especially if your alpha shaders are custom and do not have all necessary shader parameters (eg. trans)

Note: We have some pipes made of patches. Patches and models are Detail as default and don't need to be made Detail or Structure.

Screenshot #4 - Broken wall

Another example...