I usually think of street art in the way the Wiki defines it - spontaneous, unsanctioned pieces that appear, more precisely, from the street - i.e., on sidewalks, sides of buildings, parking strips, median strips, and roundabouts.
It can also refer to planned, sanctioned pieces like Seattle's Waiting for the Interurban and the Dance Steps on Broadway.
A couple of years ago, on my first visit to Boston, I encountered actual Street Art. Art on the street. The subject matter is the street itself, a bas relief of errant detritis and windblown leaves. Appreciation, however, can be hazardous to your health if, while crossing, you linger too long looking down in delight instead of continuing to the other side.
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