1971-78 Density Photograph 1971-78 Density Photograph 1971-78 Density Photograph 1978 Density Photograph In 1971 we began a series of attempts to record and fix the movement of people in certain social situations. We made photographic exposures for periods from a few minutes to half an hour on a variety of locations, the entrance to a tube station, a road crossing, telephone kiosk , a children's playground, and so on. It took us 6 to 7 years to complete the processing, but eventually we succeeded in producing density photos which indicate by colour differentiation the degrees of concentration of the people who pass.