Los Angeles

Note- Since Los Angeles is a very real city, this article will only be dealing with the city as it has been effected in the Heroic Comics timeline.

The Birthplace of Modern Heroics

While any city of comparable size can boast quite the cast of superheroes in the modern era, Los Angeles is one of the few who have any genuine claim to "being where it all began." In fact, many of the most notable heroes of the past 50 years were not just active in Los Angeles, but born there.
Golden Champion, Gladiator, Flyer Rose, Knight (Addison Reece), and both Honor Guards were born within the city limits. 

City of Origin Stories

Los Angeles' connection with the heroic element goes back even farther than anyone in the HCU realizes. It was in this city in the late 1800s that semi-vigilante law man swore to never rest until the city was safe, and doomed himself to eternal life as the haunting Spirit. 
While Lela was not born in LA, and didn't start her career there, her first big case was centred around a corrupt hollywood star [name]. After solving that case, Lela continued to operate out of LA until her death.
Eric Reese grew up outside the city, but he came to LA as a new man. It was here that he first fought as the Knight, met and married Dalia Mejía, where his daughter Addison was born, and the location of his death. This directly lead to Golden Champion and Gladiator becoming heroes in the city, and in the longer term Flyer Rose and the second knight.
While new heroes no longer catch as much attention, LA is still seen as the city to go to to make it big as a hero in California.

Heroes, Heroes, Everywhere

LA has both the highest hero population and highest hero to population ratio in the US, with New York and Miami taking second in the respective categories. Internationally, LA ranks 12th highest in hero population and 5th highest in hero to population ratio.
LA is both the centre of metahuman presence and control in the US, and the US government's efforts to control metahumans is largely based there.