For me, what is happening is the number of bread icons represents how many DIFFERT things teh tile is producing. For instance a mined desert hill will always show 1 food (it only produces hammers). A grassland hill by a river shows 3 food (it produces food, hammers and coins) all the water squares show 2 food (the produce food and coins).
Others may want to check, but i think that what we are seeing is a representation of how many of the three kinds of resources are present, not how munch of each type.
Others may want to check, but i think that what we are seeing is a representation of how many of the three kinds of resources are present, not how munch of each type.