Correction: A city plot gives the yield of the tile. If it gives less than 2 food, however, you get 2 food instead, and if it gives less than 1 production, you get 1 production. Settling a city on Plains/Hills gives you 2 food 2 production, for example. If you'd settle on a spice, you'd get 3 or even 4 food out of it, if it's grassland.