The in-game explanation of a granary is that it stores 50% of food after a population increase. But ... what exactly does that mean? First of all, 50% of what? The food on all the tiles I'm working at the time? And what does it mean to "store" that food? Does it provide instant progress towards my next population increase? Or does it provide more food for the population to consume each turn? For example: Suppose I have a city with 9 population and 20 food per turn. That's a surplus of 2 food. Thus, I am slowly but surely making progress to my next population increase. Suppose my #10 guy starts working another 2-food tile, so I'm still working on a 2-food surplus. So, when the city increases to 10 population, what exactly happens, depending on whether or not I have a granary?