Bridgehead

Bridgehead, officially the City-province of Bridgehead, is the the capital of New Sidon and the Elysian District. Additionally it's the largest settlement in the Terran Federal Republic outside of the Solar system, with a population of over 356 million. 
Located on the White Coast along the Veridian Sea, it stretches along the coast and inland around the Cardian Delta. Around a fifth of the entire Elysian District is covered by its metropolis. 
Founded to be the TSC headquarters in Alpha Centauri, it rapidly outgrew the first cities on New Sidon. It is an archetypal new city. Following the founding of the Commonwealth of New Sidon, the city was made the capital of the Commonwealth. It is a major galactic financial, cultural and diplomatic center.