Speakeasy
Where do played or excess City tiles go, and can I stack them on one space?
The designer answered this directly in the official FAQ or a forum reply.
At the end of your turn, put each tile you played, or each one over the limit of four, on the middle column of the City tile display, spread evenly and filling empty spaces first, so all three empty spaces get one before any gets a second. An earlier forum ruling that tiles could be stacked on one space was replaced by the official FAQ wording. The tiles are then available to draw.