Public space includes everything from the sidewalk in front of your house, the road on which you drive to work, and the playground in which your child plays on the weekend.  Each of these spaces was designed to achieve specific functions, and some succeed while others fail.  Just like any other part of a city, many different factors explain the success of certain public spaces, and a lot of it is context-specific.  For example, why does Rittenhouse Square always appear to be more lively than Washington Square, even though they are of a very similar size and layout?  Why is Reading Terminal always busting at the seams with people when the Kimmel Center plaza remains empty at times when a show is not playing?  Why are streetscape improvements such as widened sidewalks and street trees the key to unlocking the potential of some commercial corridors and not others?  These questions and more are part of public space planning.