Growth of Empire?

[Rockinsince87]

Is your growth of your empire passed on how many people in your empire or how many cities you have established?

- If it is based on city's then what is the minimum for a stable city as far as buildings?

Thank you guys for the help

Population growth is based on city morale. There is a wonderful explanation here with all the modifiers. 
https://www.hazeron.com/wiki/index.php/City_Morale