At least at launch, Civilization VI doesn't offer an option to play on a map resembling Earth. Modders have set out to amend this omission, but at this stage, you may not even be able to load into a game using it.
As documented on the Civ Fanatics forums by modder Gedemon, the Yet Not Another Maps Pack includes a conversion of djvandyke's Greatest Earth Map for Civ V. There's a Giant version that "is already way above the size of the Huge map" and may not load. Then there's the Ludicrous version, which is said to be the "max map size before the game refuse[s] to load." This one will take from 4-5 minutes to load (assuming it doesn't crash).
To install the mod, you'll want to download it (while being wary of what you install on your system), unzip it to the \Documents\My Games\Sid Meier's Civilization VI\Mods folder, and then activate it from the Additional Content menu in-game.
Users are warned not to try a serious game on the map until it's been more extensively tested. If you do decide to try it for yourself, it's recommended that you first go to the Video options and lower the texture sizes.
The warnings aren't to say the map is currently unplayable. Gedemon says they ran 500 turns on the Ludicrous map with 32 civs (you can go over 50) without a crash on their computer, which consists of an i7 4770K, 16 GB of RAM, and a GTX 980 Ti. If you're curious, it took three and a half hours to reach turn 240, and 14 and a half hours to hit turn 475.
Civilization VI was launched last week to a positive critical reception. You can read GameSpot's review here.