Since standing soon becomes uncomfortable, we quickly look for something to lean against or, better yet, sit upon.
Along building fronts, there is almost always something to lean against, although columns or rounded corners can be especially inviting. Along natural edges, we seek tree trunks or boulders.
As for leaning, posts near the edge of a space, or a row of posts that creates a kind of edge, prompt “the piano effect.” The name derives from the temptation cabaret singers seldom resist of sidling up to and leaning on the piano being played to accompany them. Pedestrians mimic that action with bollards, sculpture, columns, and posts along walkways and in city plazas.
Chairs and benches with backs and arms are primary seating choices. Secondary seating consists of any low, flat surface and the ground itself, which are used by children and young people on mild days when primary seating is crowded. In niches along the edge, people will sit on low walls with their backs against facades. Young people will even sit on warm, dry paving if their backs can be against a wall.
Intentional secondary seating is flat and near a spatial edge, rises between a between a few inches and 1 meter (3 ft.) high, and has views onto interesting surroundings.
In the most pedestrian friendly places, such as Venice, almost every part of the city is sittable—steps, pedestals, ledges, stones, bollards, fountain edges, or the city floor itself. When not serving as seating, they serve their original purposes of making the city an interesting place.