Most maps are automatically downloaded when you connect to a server.
However, you may require to download and install custom maps manually.
Maps are packaged with a .ZIP or .RAR extension.
This is an example of downloading a map from the VSOP Clan.
Downloading Custom Maps.
Go to https://vsop.cafe at the top right on main page is a tab maps.
Find the map you wish to install this is set out in alphabetical order.
Once you click on the map you have chosen it will take you to the download page.
Click on download and the map will be downloaded to your browsers download folder.
Installing Custom Maps.
Once you have downloaded a custom map you must make sure that the map is correctly installed.
Custom maps are packaged with the correct file names so it is only necessary to extract map folder to the correct directory.
Extracting the files you may need a program such as WinZip, WinRar or 7-zip.
Right click on the map file you download and a menu will give you options pick extract all.
Now go to your main game folder this is the default folder that you installed the game to.
Extract contents to the correct folder a following example:
C:\Program Files (x86)\Activision\Call of Duty 4 – Modern Warfare
In this directory should be a folder called usermaps. You will need to create one if there is not one there already.
C:\Program Files (x86)\Activision\Call of Duty 4 – Modern Warfare\usermaps
This is where you need to put your custom maps.
C:\Program Files (x86)\Activision\Call of Duty 4 – Modern Warfare\usermaps\mp_cgc_citystreets
Your file address should look similar to this.
Map files downloaded automatically when you connect to server may be stored else where.