Cities are as much collections of smells as they are collections of bricks: smells define them. From one block to another you can be overwhelmed by any number of odours: the garbage outside a busy restaurant, flowers on display outside a florist or freshly ground coffee as you meander past an open door to a cafe. Some city smells make you sigh warmly and think of old friends; others, like those that seep out of dank alleyways, make you skip a step and screw up your nose. Those of us that live in cities cannot avoid the olfactory messages that the streets bombard us with. Nor should we. This...