There are basically 7 types of files you'll be working with:
.map - the file you use with the map editor. It's actually just a renamed text file. It contains all of the worldspawn information as well as all of the brushes in your world (locations and shaders). You can store this file anywhere because it is not distributed, so you might as well keep it in the /maps directory.
.bsp - the playable file that Q3 recognizes. When you compile your map, a .bsp will be created in the /maps directory.
.md3 - a model file. This kind of file can be created using a 3D modeling program like milkshape, GMax, 3dMax, or LightWave. It allows you to put fairly complicated shapes and figures into your map. We've gathered some models for use in Reaction at the backlot. Once the map is compiled, all of the model geometry is incorporated into the .bsp, so you don't have to distribute any .md3 files. However, you do have to include all of the model's textures by placing them into the appropriate /models/mapobjects directory. Consult the Model Manual that came with GTK for more assistance. Read more about mapobjects on the Mapobjects page.
.shader - the file that contains all of your map's shaders. A shader is the Q3 version of a texture, but it's more than that. A shader allows you to manipulate a texture to change its color, size, shape, and give it special effects. Take some time to familiarize yourself with shaders by reading the Shader Manual that was included in the GTK download. Like the .map files, the .shader files are just renamed text files and can be manipulated with any text editor. Read more about shaders on the Shaders & Skyboxes page.
.tga - a texture file (tga is short for Targa). Targa files can have an alpha-channel, which allows for transparency. Generally speaking, all of your textures should be even powers of 2 in size (16x16, 128x64, 256x256, ...).
.jpg - another texture file. Jpg's can be used just like .tga's, except that .jpg's do not have an alpha channel. It makes no difference to gameplay which type of file is used because .jpg's are converted to .tga's as the map loads. Jpg's tend to have slightly poorer visual quality. The benefit of using .jpg's is that your map download will be smaller because the file size is smaller. There's nothing wrong with using all .tga's.
.wav - a sound file. Q3 only accepts .wav files, not .mp3's. They must be 16 bit, 22 kHz. Game sounds must be mono; level music must be stereo.
You are allowed to use any custom files, free 3rd party files, or baseq3 files. Do NOT use textures or any other files from other games or other maps unless you have explicit permission. Do not use textures that show brand names or trade marks. There were dozens of AQ2 maps made that were deemed "illegal" because they stole textures or showed trade marks. Also, do not use any textures or any files from Q3: Team Arena. You are not allowed to redistribute any id textures or files from Q3:TA to a Q3A based mod.
Make a subdirectory inside the textures and sound directories to further organize your files; use the name of your map for the subdirectory. See the model directory structure at the bottom of this page. It is important that you do not name any file a name which may be confused with any other existing file in your .pk3 or in any other .pk3. Q3 reads in every file in every .pk3 in your active directory. If it sees two files with the same name, it forgets the first one. As long as you use a unique pathing structure, you should be able to avoid conflicts.
There is a file available at the Backlot called entities.def that is required for mapping for Reaction. It's in the rq3-mapping.pk3 in the Closet. The entities.def file allows you to add entities specific to Reaction and set the behavior for the existing Q3:A entities. It should replace (back up the original) the entities.def file that came with Radiant. There is a fully commented version available on the Reaction entities.def File page.
There are several shaders available in the reaction.shader located in the rq3-mapping.pk3. Make sure a copy of this .pk3 is in whatever directory you are mapping out of. In order to use the Reaction shaders, you will have to add the line reaction to your shaderlist.txt file which is located inside the scripts directory. The specific shaders available will be explained on the Shaders & Skyboxes page.
When you wish to distribute your map, either for beta-testing or final release, you need to compile all of your map's files into a .pk3 file. A .pk3 is simply a renamed .zip file. See the Making the .PK3 page.
Your directory structure should look like this if you are mapping out of the baseq3 directory. Let's follow the racetrack example shown in the directory layout pictured below.
