Use a text editor such as notepad to edit the "Config.ini" file in your Steam Apps folder or the "\Documents\My Games\Sid Meier's Civilization 6\" directory. Find the "DebugPanel = 0" line and change it to "DebugPanel = 1". Save and close the "Config.ini" file. While playing the game, press ~ to display the console window. Enter "Reveal All" to reveal the entire map.