Connected city is just a city that has a connection to another via roads or rivers/coast (with sailing) as in vanilla. In RoM-AND (Rise of Mankind - A new Dawn) this does not generate any commerce automatically. There are no trade routes, just a list of connected cities, foreign and domestic. But you can receive commerce with the right buildings. Example: A tavern generates +1 commerce per every three connected domestic cities (up to a limit of three commerce). A port adds 4+x commerce, depending on number of domestic cities and gets a further bonus for every seafood and some luxuries in its vicinity and so on. So you don't get commerce just for founding the city, which magically creates trade routes with an obscure system and obscure revenues, but you gain commerce fitting for the infrastructure and ressources of the city. Easy to see how the numbers are calculated.