They are often boundaries defining a break in continuity between two homogeneous regions. Examples include shores, walls, rivers, and railroads cuts. Districts are the mid-sized sections of a city. They are distinguishable as having some common, identifying characteristics. Typical identifying traits include a particular architectural style, light posts, or mailboxes.
Nodes are strategic spots in the city where observers can enter.
They are typically linked to travel and may be represented by some type of transportation hub such as a mass transit station, bus stop, or traffic circle. Landmarks are point-references which are external to the observer. They are not entered into but rather are viewed from a distance. A landmark must be distinct from its surroundings and should have directional information associated with it. Directional information is essential to the navigator's ability to remain oriented with the environment.