>Here  is  an  example.  In  Berkeley,  at the  corner  of  and  Euclid,  there  is  a  drug store,  and  outside  the  drug  store  a  traffic light.  In  the  entrance  to  the  drug  store there is a newsrack where the day's papers are   displayed.   When   the   light   is   red, people who are waiting to cross the street stand  idly  by  the  light;  and  since  they have   nothing   to   do,   they   look   at   the papers  displayed  on  the  newsrack  which they can see from where they stand. Some of  them  just  read  the  headlines,  others actually buy a paper while they wait.This  effect  makes  the  newsrack  and the traffic light interdependent; the newsrack, the newspapers on it, the money going  from  people's  pockets  to  the  dime slot,  the  people  who  stop  at  the  light  and read    papers,    traffic    light,    the    electric impulses  which  make  the  lights  change, the  sidewalk  which  the  stand  on  form  a system - they all work together.

http://www.dpi.inpe.br/Miguel/AnaPaulaDAlasta/A_City_is_not_a_Tree.pdf