 A strength of observation and interaction over extended periods of time is that researchers can discover discrepancies between what participants say—and often believe—should happen (the formal system) and what actually does happen, or between different aspects of the formal system; in contrast, a one-time survey of people's answers to a set of questions might be quite consistent, but is less likely to show conflicts between different aspects of the social system or between conscious representations and behavior.Field research lies at the heart of archaeological research.It may include the undertaking of broad area surveys (including aerial surveys); of more localised site surveys (including photographic, drawn, and geophysical surveys, and exercises such as fieldwalking); and of excavation.