In order to use Maps, you need to have Extension:Validator installed.
But if you get a distribution from this page, you do not need to bother with this, since Validator comes bundled with every release, and will automatically be loaded by Maps. If you get Maps from SVN trunk, or a tag, you must make sure you also install Validator.
Once you have downloaded the code, place the 'Maps' directory within your MediaWiki 'extensions' directory. Then add the following code to your LocalSettings.php file:
require_once( "$IP/extensions/Validator/Validator.php" ); # Validator must be included *before* Maps. require_once( "$IP/extensions/Maps/Maps.php" ); # Maps
Once you have successfully installed Maps, please add your wiki to the Sites that use Maps section.