What is the importance of city sidewalks and streets in the book, The Death and Life of Great American Cities?

Sidewalks and streets function as a place of movement for vehicles and people, but additionally, the safety element must be taken into consideration. A city is considered unsafe when its citizens don't feel safe on its streets and sidewalks. What makes the streets safe are the surveillance, presence, and actions of the residents of those streets. Diversity is needed in a neighborhood and sidewalks and streets contribute to that diversity by the variety of people with different uses that use them.