So, from that PDF: Page 7. City Improvements. (right hand column)
"The first improvement in each area always costs 1 commodity of the matching type. The second improvement in each area costs 2 of that commodity. The cost of each subsequent improvement is again increased by 1. "
So, to elaborate, the first city improvement costs 1 commodity. The second 2; third 3; etc. If you have more of the correct and matching commodity (and a city, as stated further in the rules) then you can do as many improvements as you can afford per turn. Example: if I have 6 paper, I can make the first, second and third city improvements for "instants" aquaduct.
I would love to jump over the lower improvements and get a metropolis right away, but alas, we have to pay for it. I hope that helps.
@denis_eps Yes you can use the options menu (in game). Apart from that we are currently working on an improved "so called" vs. Screen which will enhance the UX for the players (giving more info on what scenario is played and so on)
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