Focusing on people side, there are also two kinds of area in the street, pedestrian and people who belong this area. Pedestrians are similar to cars on the road and they make a stream on the walkway. (image blue part)
On the other hands, there are other people around the area such as worker of building construction, students, business officers, and people who live around there. Those people sometimes create small invisible area when they have a lunch in a small group, for example, a worker of building construction buy a lunch box and eat with co-workers together on the walkway, and they create small personal space. (image upper right) There are also students chatting at the corner, business man talking with cellphone, and people walking around with dogs. (image bottom area) The walkway does not have such a strict rule compared to the road, so people on the walkway create personal area(s) and stream line(s) freely.
At this point, people who create personal area are also observers while they are doing something on the walk way. For example, some workers were watching me (us) and they might be thinking that what we are eating lunch at that time.