In Civilization 5, how is the amount of food or production received from domestic trade routes calculated?
They are static rates (not affected by tech/buildings/etc). It's 4 for land routes and 8 for ships. The base city doesn't lose that food or production, the other city just gains it, which is nice.
EDIT: The 4/8 number is a base value. It increases incrementally by a value of .5 for each age advancement starting at Renaissance era (need to check the age to be sure, will test in a game when I get a chance).