Early in the game I got a combo by following a specific recipe of placing buildings next to each other: Eye Glasses store, Fruit Stand, Flower Cart. This created some huge windmill thing on top of the fruit stand, and apparently I get bonuses to the shops for arranging them this way. Is there a generic formula, or some other way I can determine how to arrange buildings to get these bonuses?
According to here:
Note that in some cases, you will also need to upgrade a building a few times to be able to make a combo with it.