The Philadelphia Streets Department (PSD) conducts street litter surveys several times each year. They use a Street Litter Index to assign as score (1 – minimal, 4 significantly littered) to rate small multi-block survey areas.
Here are side-by-side maps of PSD’s 2007-08 and 2012 surveys:
(Click to enlarge)
You can compare these 2 maps in a before-after fashion by clicking this image and moving the Vertical slider: (Click to see interactive version)
Notice the differences between 2007-2008 and 2012? Any ideas why 2012 looks like there is less litter?
Here is a short Word file on the Street Department’s Litter Index ( psd_street_litter_index)