It's not a city ordinance at all but it is however quite complicated and lots of "grey areas", the stuff is basically illegal up until the point it magically appears in the coffeeshop, and then it's illegal over 5g. In any case traveling with it internationally is a big no-no even if it's between two destinations where it's legal. This is all very silly of course, hopefully with Germany going legal we're finally gonna start seeing some progress on the topic, if daddy Germany is ok with it the rest will likely follow.