The famous book by Kevin Lynch spells out a theory of urban form that makes use of five organizing principles: path, node, edge, landmark, and district. Lynch suggests that a city with a recognizable, memorable image will have clear and well-defined elements in these five categories.
- Paths are how people move through the city in one of various transportation modes. Modes may be coordinated or disjoint; vehicular routes may be the same as pedestrian routes or subway routes, or may be different.
- Nodes are generally at the major intersections of paths, but are most characterized as gathering places and interchanges where people may linger.
- An edge separates one defined part of the city from another.
- A landmark is a place that has a strong visual identity. It may have a presence on the skyline, or may simply be a place that people use to orient themselves and measure distance.
- Districts are memorable neighborhoods within the city. They may be functionally associated, (such as a residential district, the Central Business District, the meat-packing district), or they may be more self-contained to include residential, recreation, and work all in one cohesive unit.
Lynch and his students analyzed a few cities, but their empirical studies are somewhat inconclusive.