In Civilization V some buildings or policies affect local happiness, while others global. What's the difference? I understand local means per city, but does it have any different effects towards the total happiness of your empire than global does?
Local happiness is the same value as global happiness but is capped by population. So if you have 6 possible local happiness in a city from buildings, but the city is only 5 population, you only receive 5 happiness. When your city increases to 6 then you will have 6 local happiness in the city. This prevents a city from providing positive happiness