Earth

Earth (地球) is the main setting and backdrop for the Mega Man franchise. It is the third planet from the Sun and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets. It is sometimes referred to as the world or by its Latin name, Terra. Earth is home to millions of species, including humans. Both the mineral resources of the planet, as well as the products of the biosphere, contribute resources that are used to support a global human population. These inhabitants are grouped into about many independent sovereign states, which interact through diplomacy, travel, trade, and military action.

Original Mega Man universe
In the classic Mega Man series Earth has many similarities with the non-fictional Earth, but has much more advanced technology and, if Wily and Right's RockBoard: That's Paradise is taken as canon to any degree, different names for continents and/or nations. The whole planet and maps of it can be seen in many games, especially in the stage select screens from Mega Man 8 and Mega Man X5 to Mega Man X8.

In the 21st century, with the advancement of science, humans were able to create industrial humanoid robots to help with different tasks, and they coexist peacefully. However, in the first Mega Man game, the scientist Dr. Albert Wily plans to take over the world, and the foremost authority on robotics, Dr. Thomas Light, modifies the helper robot Mega/Rock into the super robot Mega Man (Rockman) to stop Wily, starting a series of battles between the two scientists and their creations, nicknamed by fans of the series as the "Robot Wars".

At the end of the wars, Dr. Thomas Light created a robot he named Mega Man X, which is able to think and make its own decisions. He was sealed after then because of the fear of how dangerous he can be to the world. After the discovery of X 30 years after, Dr. Cain created Reploids based off X's design. The world eventually turned into two great major factions: Reploids and humans. They lived peacefully for a long while. Unfortunately for Dr. Cain, Dr. Light’s greatest fear came true. The presence of Maverick Virus causes the new robots to rebell against humankind and became powerful enemies known as Mavericks, showing hostile actions against the world's peace. The group was eventually developed larger under control of Sigma, which was stopped ultimately thanks to Maverick Hunters X and Zero.

Shortly after the end of the long lasting Maverick Wars, the Elf Wars occur, a four year long conflict that ended with approximately 90% of all Reploids and 60% of all humans dying. After the war, Maverick Hunters X and Zero have vanished from the view of the public and have become mere legends. Humans and Reploids find themselves at war as the humans have decided to stamp out all of the robots that caused the wars of the past. Two factions emerge: some Reploids continue to serve the humans, even though the humans are in the process of systematically destroying most of the Reploids. The rest of the Reploids have fled, creating a Resistance force in an attempt to save themselves from annihilation.

Ciel, a human scientist, by studying Cyber-elves, hopes to develop a new source of energy that she intends to use to bring peace between the Reploids and the humans. Until then, they fight. Ciel revives the ancient warrior Zero, who had been locked away for an unknown span of time. Zero finds himself facing the past when he battles Copy X, a duplicate of his historic partner, and leader of Neo Arcadia, the primary human government. The original X appears, in the form of a Cyber-elf. His body was sacrificed in an attempt to imprison the Dark Elf, the source of the Elf Wars. Now X serves primarily as a source of guidance. Meanwhile, Dr. Weil, a scientist banished from Neo Arcadia for instigating the Elf Wars using a Reploid known as Omega, returns with a vengeance to attempt to accomplish his goals once and for all. He takes over Neo Arcadia and makes prisoners out of the humans as much as he wages war against the Reploids. He and his plan was ultimately defeated with the heroic sacrifice of Zero.

After the fighting against Neo Arcadia came to an end, Ciel and her research team comes across the remains of Doctor Weil's remain core, also called Model W, begins to turn members of Ciel's team into Mavericks. Dr. Ciel's fate is unknown, so Alouette, a young Reploid raised by Ciel, assumes command of the Guardians. A new law is created by the Legion, were Reploids must have lifespans and humans have mechanical parts integrated into their bodies, and now both are treated equally as humans, living together in harmony. One member of the Sage Trinity, Master Albert, created the Game of Destiny and made Mega Men fight against each other by using Biometal, which was created by Ciel from analyzing data of heroes from the past, and finally against Albert and Model W.

Several thousand years later, Earth (known as Terra outside Japan in the Mega Man Legends series) was covered by water, and humans now live on small landmasses. The original humans live on Elysium while bionic humans known as Carbons live on Terra. Before dying, The Master asked Mega Man Trigger to protect the Carbons and destroy the System, resulting in a series of battles that ended with Mega Man and Sera being sealed by Yuna for several years, and those events became legends. One day, the Digger Barrell Caskett found Mega Man Trigger sealed in a ruin and adopted him, naming him Mega Man Volnutt.

Mega Man Battle Network universe
Unlike the original series, the locations of the Earth from the Mega Man Battle Network and Mega Man Star Force series use fictional names, but still share many similarities to the real life Earth.

In 200X, most people have a PET (PErsonal Terminal) with a NetNavi. Humans use the humanoid NetNavis housed in their PETs for general use as Operators, although some work with their Navis in a sport called NetBattling, where an Operator uses Battle Chips to give their Navis special abilities to fight with, such as giving a sword or bomb. The series is centered around young Lan Hikari and his Navi, MegaMan.EXE, who both love to Net battle, and their adventures in the world, such as participating in a tournament (third and fourth games), or stopping a Net-criminal organizations like World Three, Gospel and Nebula.

200 years later, the Internet-based technology was replaced to an EM Wave-based technology, which created the Wave Road exists in the real world, EM Beings replace NetNavis, and no one uses a PET anymore. They're all invisible to human's vision. With the use of three satellites, controlled by the Satellite Admins, the whole Earth is connected using the Sky Wave (and later the Astro Wave), which transcend to space (Outer Astro Wave) and other planets, such as Planet FM and Planet AM. The series centers around Geo Stelar, a 12 year old boy who lost his dad Kelvin Stelar in a space accident, and the fugitive AM-ian, Omega-Xis, who can change Geo's frequency in a way called EM Wave Change, who lost his father, fighting villains such as other FM-ians and other antagonists, such as Le Mu and Dealers and finally found him in Meteor G core.

Trivia

 * If Eurasia crashes on Earth Mega Man X5, the picture of Earth in the stage select screen will drastically change, showing how much damage it suffered. However, Earth has its original appearance in Mega Man X6 onward, showing that canonically the impact's damage was reduced by the efforts of the Maverick Hunters.
 * In Mega Man Legends, there is an old world map on Barrell Caskett's room that is different from the Earth shown in the classic and X series, but Mega Man Volnutt says it is different from the planet's current appearance.