A bunch of users have told me of strange compiling errors. Fear not, I have a solution! Here's what I use to compile the map:

***NOTICE*** If the steps below fail to work, try using the Hammer/BSP/VIS/RAD applications that come with Garry's Mod, found in GarrysMod\bin .

Under "Library" is a section called "Tools". Look for the program mentioned above, and install it. Once installed, look for Hammer in "steamapps>common>Source SDK Base 2013 Multiplayer".

In Hammer, open the "Tools>Options". Create a new configuration for Garry's Mod (if you don't already have one). Here are my settings:

• Game Data - $SteamUserDir\GarrysMod\bin\garrysmod.fgd
  
• Game Executable Directory - $SteamUserDir\GarrysMod
  
• Game Directory - $SteamUserDir\GarrysMod\garrysmod

Now, in the Build Programs tab...

• Game executable - $SteamUserDir\GarrysMod\hl2.exe
  
• BSP/VIS/RAD executables - $SteamUserDir\Source SDK Base 2013 Multiplayer\bin\<program>.exe
  
• Place compiled maps in... - $SteamUserDir\GarrysMod\garrysmod\maps

Find the GameInfo.txt file in "steamapps>common>GarrysMod>garrysmod". Replace the file's contents with the steampipe-revised version (you can find it on the internet). Then obtain an unpacked copy of Counter Strike: Source's resources. Copy CSS's materials folder, and place it in "GarrysMod>garrysmod". This should merge the folders together, and certain materials will be overwritten. To prevent eternal sadness, just make a backup of your GMod materials folder before merging the folders. Do this for each folder you need to borrow from CSS.

... Aaaaand you're done! The map should compile properly now! Have fun!