Analysis of the results identified three physical features that help explain the apparent split between tranquillity and preference. These were; mistiness, unstructured openness; which refers to how open the scene is and how difficult it is to establish a sense of depth or distance, and surface calmness. Mistiness and unstructured openness tended to depress preference relative to tranquillity whilst surface calmness tended to enhance it. Herzog and Barnes conducted a follow up study in which deserts and waterscapes were included in the setting types. In 2000, Herzog and Chernick conducted further research into the tranquillity construct when they investigated the relationship between tranquillity and danger in urban and rural settings.