the idea: trace the outline of shadows during the day so that they remain when the sun goes down

A while ago I was walking up Mass Ave in Cambridge when I realized that there was something on the sidewalk.  Drawings.  But not just any drawings, these were drawings attached to objects and I quickly realized that they were shadows.  Not only that, but the shadows stretched all the way up the street.  For over two block.  There were inanimate objects but also people standing around, doing normal things.

I forgot to ask about this when I actually saw it, but I’ve been curious about whose idea it was since then.  If anyone knows, please send it along!