People from earth are sometimes known as Flatlanders and are considered naive and arrogant by the rest of the galaxy, having grown up in an environment that was tailor-made for them. Earth's 18 billion people seem to devote a lot of their time to goofing off and wearing exotic fashions, including exotic skin dyes and artificial eye-and-hair coloring.
Earth is ruled by the U.N. and its Amalgamated Regional Police, or the ARM. The ARM are technology police, making sure no dangerous new weapons are built and deployed. They also controlled the illegal practice of organlegging until prosthetic technology outpaced transplant technology. More recently the ARMS became involved in "extremely foreign relations," handling contact with alien races (for example, pushing the Kzinti off of Wunderland and monitoring the Puppeteer retreat from Known Space).
Notable Flatlanders: Gregory "Elephant" Pelton, Lucas Garner, Gil "The Arm"
Hamilton, Carlos Wu
For Further Reading: "Flatlander," Ringworld, Flatlander
A separate entity but ruled along with Earth by the U.N., the moon has several major cities and customs of its own.
For Further Reading: The Patchwork Girl, "The Woman in Del Rey Crater"
When the miners in the Asteroid Belt completed work on Confinement Asteroid, the first large bubble-world, they declared independence from Earth and the United Nations. Several years of tension followed, but eventually an era of trade and prosperity set in, not threatened until the arrival of the Kzinti.
Notable Belters: Jack Brennan, "Lit" Shaeffer
For Further Reading: World of Ptavvs, Protector, "Madness Has its Place"
Very few humans live on Mars. The Martians killed the first explorers, before they themselves were wiped out by the impact of a water-laden comet on the red planet's surface. Even though the Martians are now extinct, almost no one goes to Mars except archaeologists because it contains nothing of value that can't be more easily obtained elsewhere in the solar system.
For Further Reading: "Eye of an Octopus," "How the Heroes Die," "At the Bottom of a Hole," Protector
Mercury would be utterly uninhabited if not for the crews that maintain the giant launching lasers that were built there to push the first colony ships out of the solar system. These lasers found a second use as defensive weapons during the Kzinti attempts to invade Sol.
For Further Reading: "The Coldest Place," "Madness Has its Place "
The first human colonies were explored by ramrobots, unmanned probes that sought habitable landing sites. Thus, some settlements in Known Space exist on worlds that are only partially habitable, such as Jinx and Plateau, or habitable only for part of the year, such as We Made It. The following is a partial list of explored and colonized worlds in Known Space.
Jinx is an oblong moon, pulled out of its round shape by its proximity to Primary, a gas giant orbiting the star Sirius. The equatorial region is shrouded in high-pressure gas, and no one goes there except to hunt Bandersnatch. The Ends stick out of the atmosphere entirely, providing centers for vacuum-based industry centers and spaceports. Between the Ends and the center are two bands of habitable living space.
Jinx has more mass than Earth. Over the years, the people of Jinx have evolved into a squat, stocky race, as wide as they are tall, and very strong compared to humans, though they tend to die younger. Jinxians are horrible punsters.
Notable Jinxians: Dr. Julian Forward, Emil Horne, "Captain Kidd" (real name unknown)
For Further Reading: World of Ptavvs
The closest colony to Earth, Wunderland is a fairly Earth-like world. The "19 Families" who landed with the first colony ship declared themselves an aristocracy, and vestiges of their attitude can be seen today in the unique asymmetric beard worn by many of Wunderland's upper class. A strong germanic tradition pervades the society; the capitol city is called Munchen.
Wunderland suffered for many years under Kzin occupation during the First Man-Kzin War. In the years to follow, Wunderland has produced some impressive technology, including amazing kitchen computers for use on starships, and the Wunderland Treatymaker, one of the few weapons that can actually cow Kzinti into surrender (or so they claim). The U.N. has had a foothold on Wunderland since retaking the planet from the Kzinti, which has led to various underground "Free Wunderland" movements and even a revolution by Louis Wu's time.
The Serpent Swarm is Alpha Centauri's asteroid belt. It is not actually a full belt but a semicircle, hence the name. The capital asteroid, Tiamat, houses a large postwar Kzinti population.
Oh, and some Wunderlanders, notably the aristocracy, have highly moveable ears.
Notable Wunderlanders: Richard Schultz-Mann
For Further Reading: Protector, "A Relic of the Empire"
The first colony ship to Procyon crash-landed. The city that grew up around the wreck was called "Crashlanding City" and the planet was dubbed "We Made It" by its citizens, known from then on as Crashlanders. Procyon's axis points along the plane of the ecliptic, and for half of the year the planet is whipped by ferocious winds. The citizens live underground, and about 40 percent of them are albinos. But the planet's lower mass has allowed them to grow up tall.
Notable Crashlanders: Beowulf Shaeffer
This venus-like world would be uninhabitable but for Mt. Lookatthat, which rises out of the soupy, misty atmosphere into a temperate layer, and has a livable surface area on top that's about the size of California. Citizens of Plateau are sometimes called Mountaineers.
The crew of the first colony ship to Plateau, the Planck, declared themselves the ruling class upon landing and forced a social order upon the newly-thawed colonists. When the Arthur C. Clarke landed a few years later, its passengers were forced to adhere to the same code. The Planck, the Clarke, and the Hospital became the center of the Crew high society; colonists were easy to control because they relied upon Crew for medical care and transplants. Colonists who disobeyed the law went into the Organ Banks. The arrival of cheap medical technology from Earth spelled the beginning of the end of the Organ Banks, sparking a revolution that ended with the destruction of the Planck and the end of the social stratification.
Notable Mountaineers: Matthew Keller
For Further Reading: A Gift From Earth, "The Ethics of Madness"
This Earth-like colony "failed" and was quarantined when Jack Brennan seeded the atmosphere with his variant of Tree-Of-Life in order to raise an army of protectors. Most of the population was killed by Brennan's virus, and the planet itself sustained some damage in the subsequent battle with a Pak scout ship.
By the time of Beowulf Shaeffer, several hundred years later, Home has apparently been re-settled.
For Further Reading: Protector
This jungle world is popular with hunters. The sessile "Gummidgy Orchid-Thing" is a carnivorous beast that hangs on tree branches awaiting prey. They are popular decorations of the wealthy.
For Further Reading: "Grendel"
Three large patches of Slaver Sunflowers dominate the view of Silvereyes from space. Seen from certain angles, the Sunflowers fields can resemble shining silver eyes.
For Further Reading: "The Color of Sunfire"
This low-pressure world was a former Kzin holding until it was hit with the "Wunderland Treatymaker," basically two modified Slaver disintegrators run in parallel 20 miles apart, which dug a huge furrow in the planet's surface. The atmosphere in the manmade canyon is breathable, and there is a sea at the bottom. People live in abodes set into the walls of the canyon.
For Further Reading: The Ringworld Engineers
A former Kzin world until given to humans in reparation following a war. Home of Grogs. In orbit around Down's sun is a remote-control ramscoop that will fire into the sun if it ever becomes known that the Grogs pose a threat.
For Further Reading: "The Handicapped"
This former Kzin holding is mostly ocean. The one continent is called Shast, a Kzin word meaning "burrowing murder." Humans and Kzinti live side-by-side on the surface and in underwater cities.
For Further Reading: Crashlander
Margrave is only in the first stages of colonization late in the Known Space timeline. "Rocs" are enormous birds native to Margrave.
For Further Reading: "Safe at Any Speed"
An uninhabitable ice world.
For Further Reading: "The Soft Weapon"
A colony established by rebellious Kzin telepaths and humans seeking to escape the first Kzin incursions into human space. Its location remains a secret, though the Patriarchy would dearly love to capture the entire population of potential Telepaths and press them into service.
For Further Reading: "Fly by Night"