Alley may be paved, or unpaved, and a blind alley is a cul-de-sac. Modern urban developments may also provide a service road to allow for waste collection, or rear access for fire engines and parking. Because of geography, steps (stairs) are the predominant form of alley in hilly cities and towns. This includes Quebec City in Canada and in the United States Pittsburgh (see Steps of Pittsburgh), Cincinnati (see Steps of Cincinnati), Minneapolis, Seattle, and San Francisco as well as Hong Kong, Genoa and Rome. Some alleys are roofed because they are within buildings, such as the traboules of Lyon, or
Balmy Alley Norris. The Balmy Alley murals have been described, along with San Diego's Chicano Park and Los Angeles' Estrada Courts, as a leading example of mural environments that reclaim spaces for Chicanos and give expression to a history of Chicano displacement and marginalization. The mural grouping in the alley is internationally recognized, both as an exemplar of activist art and as a tourist destination. The Mission District has San Francisco's densest concentration of murals, often along political themes, sometimes described jointly as the "Mission School" of muralism. Balmy Alley is often cited as the leading concentration within the Mission. Nearby Clarion