Create a rule called Commercial Zones as a subrule of Architected Cities:

A city architect can create a commercial zone in their city at any time, up to their maximum. The default maximum number of commercial zones for the city (known as the Commercial Cap) is 0, but is increased by the following factors:
* A city has +1 Commercial Cap if they have at least 1 Industry Zone, and their Region has a Primary Resource. (They are said to be Producing this Primary Resource, if they meet this condition.)
* A city has +1 Commercial Cap if they have at least 2 Industry Zones, and their Region has a Secondary Resource. (They are said to be Producing this Secondary Resource, if they meet this condition.)
* A city has +1 Commercial Cap for each distinct Resource that they themselves are not Producing, but is Produced in cities that they have a Transit Link to.

If a City ever has more Commercial Zones than their Commercial Cap, the excess Commerical Zones are turned into Dilapidated Zones in that city.

If the proposal Blaze the Trails failed, delete the third bullet point in the rule Commerical Zones.