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Another picture from Market Street in San Francisco. A long-exposure photograph is a great data-collection tool. It can reveal how much interaction there is with any given subject: the more people are in a given area the stronger their traces become in the picture, or the longer people stay in one spot the more solid their features appear. In this case, no-one was interacting with the homeless person that was rolled into a blanket behind his wheel chair. Yet, a few people passed by so closely to him that they nearly stepped onto the pizza box lying next to the wheel chair.