Actually, your citizens do not have to work land. With 1-5 citizens, any not working land produce 1 hammer. With 6-10 citizens each one not working a tile produces 1 hammer and 1 arrow. As you cities get bigger, non-assigned workers get better. The one thing they do not do is produce any food. Ever. This is the secret which underlies the Super City Strategy. If you have 20+ people in one city, each one is far more productive than any ordinary land space and better than most resource tiles. On top of that, with one super city, you only need one market, one temple and so on. It is also the reason why this game makes food the most important resource by far. It is the only resource which cannot be produced in copious amounts by the "unemployed."