Thank you MarkG, now I have answers to all but one of my questions:
if my city is squeezed in between other cities and the city radius is cropped short, will I still need the same number of population that I would need if it was free in order to harvest 100% of resources? If for example another city prevents my city to gather resources from 3 squares that would have been inside its radius but are controlled by the other one, will I need 3 less workers to gather the full resources?
In this case, what will happen of the extra 3 workers? Must they be specialists forever or could they be used LATER to gather resources when eventually the radius will grow another ring?
I think nobody asked this before. I will await an answer also to this last doubt (for now
). Thanks again for the quick answer.