How are a city's combat strength and hitpoints determined?

Question

The combat strength of a city seems to slowly increase overtime with the population, but that's just a guess. I'm curious what is the exact formula for determining the combat strength of a city?

Obviously buildings like walls or a castle have the most direct impact. And I know that social policies, like Universal Suffrage, can also have a strong impact on the combat strength and hit points of a city.

But that still leaves a lot of unknowns about how the combat strength and hit points of a city are calculated. Some cities seem a little tougher than others in terms of their combat stats.

Does anyone know the base formula's for a city's combat strength and hitpoints?

Or have an idea of the major components of the formula?

(Side question: is Terrain a major component?)

Answer 1

The combat strength of a city is determined by population and terrain, and is then effected by any defensive buildings built inside of it and social policies selected by its ruling civilization. Garrisons inside of cities also boost its combat strength. Hit points are the same way, but they're not effected by garrisons.

Source