.CIV5MAP File Extension

Map file created by Sid Meier's Civilization V, a civilization-building strategy game and the fifth game in the Civilization series; contains pre-made or custom data that specifies features of playable maps, such as map size and location of available resources.

In Windows, your CIV5MAP files will be located in one of the following directories:
My Documents\My Games\Sid Meier's Civilization V\Maps
or
C:\Program Files (x86)\Steam\SteamApps\Common\Sid Meier's Civilization V\Assets\Maps

On a Mac, your CIV5Map file will be located in the following directory:
~/Library/Application Support/Sid Meier's Civilization 5/Maps