Locate all the white maps Tier 1 - 5 on the atlas, view the atlas, and identify the maps that have not been completed.
Then procure all of the maps by trading with players, drops or through zana.
You can use additional websites such as poe.trade to locate vendors in game, or use the official trade channels.
Defeat the boss inside the map to complete it. You can collect a number of maps and run them all with a team for fast effective completion.