This page contains spoilers up through episode 34
Haixing is the name of the planet on which the drama takes place.
The Dixingren chose to stay underground, which is how they received their name. The underground climate caused them to experience a chemical reaction that led to genetic mutations. So while they looked like the inhabitants of Haixing, they developed powers that gave them various abilities such as controlling water, thunder and lightning, decomposing natural materials, and controlling human will. Their numbers were far less than those of the Haixingren. (ep01)
The three groups lived peacefully until a meteor crashed and destroyed the ecosystem of the planet. The resources of Dixing started to deplete, so the Dixing people started escaping above ground. Some of them started to invade Haixing and Yashou lands for resources and war broke out. (ep01)
The allied forces of Haixing, Yashou, and a small group of Dixingren won the war against the rebel Dixingren. The four Hallows were the deciding factor. They were created with the powers from the meteorite.
The Haixingren stayed on Haixing.
Dragon City (龙城, Lóng Chéng) is where most of the drama takes place. It was built over the hollow in the ground that was created by the "aerolite" (?), so the connection between Haixing and Dixing is there. (ep34)
Places in Dragon City
Dragon City University (including Shen Wei's Office)
Zhao Yunlan's apartment
Shen Wei's apartment
Zhu Jiu's Hideout
Near Dragon City? Where Fourth Uncle and the rest of the snake tribe live.
within a day's drive of Dragon City -- includes Qingxi Village
Most of the scenes set in Dragon City were filmed in Shanghai Film Park. The mountain scenes during the Hanga arc and the war 10,000 years ago were filmed in a mountain in Suzhou (Source).