Earth

Background
The homeworld of the human race and the most populous planet in the solar system, Earth has seen more than its fair share of history of blood and turmoil. The planet was devastated by the Warp War in the 2070s, leaving the surface a desolate, blasted wasteland. It took decades for the planet's reconstruction and recolonization to commence in full swing, and it was only possible by using the same technology used to terraform distant worlds to clean the Earth's atmosphere. Thanks to policies set by the Neo-Earth Directorate, the planet's population exploded in only a single generation, with the vast majority of people having been born in artificial wombs. This trend continued with each proceeding generation, but the Neo-Earth Directorate refused to change its policies, sure that the larger the population, the more inured humankind would be to the potential of self-annihilation.

In order to make room for more and more citizens, the Neo-Earth Directorate utilized its newest invention: constructive nanobots. Countless tiny machines capable of synthesizing materials on a molecular level and carried by a 3km long mobile space station called a Drone Fabricator, constructive nanobots swarmed the Earth. Entire regions of the world were built over in mere days, and the construction efforts only increased in speed and scale over time. By 2140, the entire planet was encased in a metal sheath and huge sections of the planet's crust had been hollowed out. Future Forward Corporation designed the world-wide arcology that the planet was slowly transformed into, as the metal surface was layered over with another level, and another, and then another, over and over again.

As layers of city were planted on top of eachother one after another, the population moved with them. The wealthy preferred to stay on or near the surface, while the poor could not afford to. Although the construction finally ended in the beginning of the 23rd century, the disparity in living conditions only grew larger and more apparent with time, and by the year 2308 AD, many regions of the lower levels were all but abandoned by the government.

Layout
The Earth arcology, named the Earth Supersphere by its designers, is a 118-level high structure made of steel, plastic and concrete that encases the entire world. The levels do not necessarily encompass entire bands of the surface or crust, as there are spaces in between them for inter-level highways, magrails, vaccuum tube elevators and all of the myriad machinery necessary to make the arcology livable. Orbital elevators are spaced out along the equator, connected to a thin orbital transit ring leading between a litany of habitable space stations in low earth orbit, with most primarily used as space docks. Underground, most levels of the planetwide arcology have enormous sunlamps planted in the ceiling and fans the size of skyscrapers pushing the air around to simulate a pleasant breeze. The temperature and weather are totally artificial, and there has been no rain on Earth in a century and a half. The planet's administration is split into districts, with a total of 195 districts per level, each representing a distinct cultural region based on the nations that existed there in the 21st century. The levels built beneath and above 21st century New York, for instance, are all referred to collectively as "Neo-New York," the population there is primarily English-speaking and of American cultural heritage. Officially, there are a total of 23,010 individual administrative districts on Earth.
 * Level 118 - The surface. The wealthiest, nicest part of the planet to live. The most recently constructed level, with the largest buildings.
 * Levels 90-117 - The upper levels. Construction completed in the 2190s. Very wealthy, it is the second most populous region of the Earth Supersphere and home to many universities, corporate facilities and government agencies.
 * Levels 72-89 - The upper-middle levels. Construction completed in the 2180s. Fairly wealthy in parts, but with a much larger degree of variation in incomes than the levels above it. The most populous region of the Earth Supersphere, with the most residences and service jobs.
 * Levels 55-71 - The middle levels. Construction completed in the 2170s. At one time, it was the most populous part of the Earth Supersphere when level 70 was the surface layer. Now, it is where most of the lower-middle class lives. As one descends through these levels they become smaller with ceilings closer to the ground, with smaller buildings made with older materials and techniques, and less open space in general.
 * Levels 38-54 - The lower-middle levels. Construction completed in the 2160s. Though not as populous as the levels above, these levels are the most densely populated, with the majority of residents living in tightly-packed tenements. Living conditions on these levels are generally poorer than those above, with rampant crime, poor social safety nets and ineffective government services. Most of the machinery responsible for pumping air and generating electricity for the arcology is located here, as well as a large number of factories and other production facilities. Level 38 marks the surface of the Earth's crust, also termed "sea level," though the planet has no seas.
 * Levels 12-37 - The lower levels. Construction completed in the 2150s. Extremely impoverished, sparsely populated, and full of condemned buildings. This area has dramatically poorer living conditions than higher levels, despite having more room than the lower-middle levels due to the smaller populous. With poorly maintained infrastructure and a total lack of any government services or oversight, the lower levels are essentially in a state of constant near-anarchy, tempered only by the organized criminal syndicates that control them.
 * Levels 1-11 - The abandoned levels. Construction completed in the 2150s. Not officially inhabited, though there are many homeless here. Consists almost entirely of abandoned infrastructure and factories, with some living facilities sprinkled throughout. Completely invisible to the UEF government, the abandoned levels are a hotspot for criminal activity and for escaped androids or mutants hiding out.
 * Level 0 - The very bottom layer of the Earth Supersphere. Construction completed in the 2140s. Though knowledge of it is common, its contents are the subject of urban legend and myth. It has been over a century since the last official visit to the bottom, and urban explorers who have tried to reach it have repeatedly reported the absence of any accessible entrances.