One series, "A Love Letter for You" by artist Steve Powers, includes 50 rooftop paintings. Photo by Adam Wallacavage, City of Philadelphia Mural Arts Program

Los Angeles plays a huge role in the street art world. The mural "I was a Botox Junkie" was painted in 2013 by artist Tristan Eaton in LosAngeles. Photo by Matt Marriott, Discover LA

Los Angeles' arts district is a hot spot for new public works of art. Photo: Matt Marriott, Discover LA

Street art blossomed in New York in the late 1970s and 80s. Photo by Kathleen Fox

Today, street art flourishes across New York City, particularly in spots like Williamsburg and Bushwick in Brooklyn, along with the Meatpacking District and the Lower East Side. Photo by Graff Tours