One possible form of a sound map, made during two different time periods on a “listening walk” around a city block. The different types of sounds are given graphic values according to whether they are soft, medium or loud, and tabulated to show the general activity and intensity. Using this method, it is simple to make comparisons of sound events historically or geographically.

Schafer, Murray R, The Soundscape- Our Sonic E…, loc. 887