The correct answer to this open question is the following.
You did not include the map so we have no reference for it. However, doing some research to find maps of that ancient time, we can comment on the following general terms.
Based on my knowledge of the geography of ancient Mesopotamia, the two cities that would be most likely to engage in a thriving agricultural trade could have been Babylon and Kish.
These two cities were so close and developed agricultural techniques that allowed them to take advantage of the flooding of the Tigris and Euphrates Rivers to grow crops in that fertile land. Another important agricultural trade relationship could have been between Ur and Eridu, important city-states in the south region of Mesopotamia.
