what I meant was....
If you have *A* city producing workers with some number of coins available and do this over time, you will reach a population level that will bounce back and forth between.
Assume you one shield production, that will take 10 turns to complete a worker. Now, at some point, a city will need 10 turns to grow. If it is 9 turns, the city will increase in size... eventually. If the time to grow is 11, the city will shrink in size.
The smaller the city, the faster it grows. having a large amount of shield producing bonus(factory, plant, mfg plant), you can depress the population much lower than you can without these buildings.
ok, going to try to fudge an example here... My math will be off but its the concept and the *edit* exact numbers are not*edit* relavent.
below size 6, requires 2 stacks of food to grow and half that with a granery. It also requires 10 shields to build a worker.
A floodplain with railroads and in democracy will produce 4(?) food. ok, so how many people will that support? ->4 tiles. Its the base city + one person + 2 from the flood plains. This is with zero growth.
Now, if you have a second flood plain for growing that pop up, how many tiles worked:
1 for the city, 1 for that person in the city, 4 which include 2 flood plains and you may have extra food unless they are put to work on a mountain. This would be 5!
ok, i swear i am going someplace with this commentary.
lets assume that the city produces 1 shield, there are 2 of your 5 are working floodplains. This allows 3 people to work grassland. the grassland is mined. For arguement sake, the grassland produces 1 shield on each of 2 tiles and 2 shields on 1 of the tiles. This is 1 from the city + 1*2 + 2*1 or 5. Assume that our *production* bonus is 100%. Therefore a worker can be produced in one turn.
On the food side, this grassland is growth food. the floodplains support the base population. So, 3 grassland gives 6 food or a growth in 2 turnsish.
Summary, your pop will go down by one then up by one. Building a worker every other turn. If you had three floodplains, the numbers would work out differently.
This is not an exploit but a strategy of either building workers or transfering population from a city which has fast growth potential to a slower growing city.