This type of mark appears when buried features, such as the ditches and banks of an ancient settlement, affect how plants above them grow, causing them to ripen at a different rate to the surrounding crop. The result, seen from altitude in the right light and season, is a faint but legible outline of a world otherwise lost underfoot.

What the aerial photograph captured in July 1989 is consistent with a rath, the Irish term for a ringfort, the most common type of early medieval settlement in the country. A rath typically consisted of a circular earthen bank, known as a fosse when referring to the surrounding ditch, enclosing a domestic space where a farming family would have lived, kept animals, and carried out daily life, generally between the sixth and twelfth centuries. The Ballyhooly example appears to have been a modest one: the enclosure measures approximately twenty-five metres in diameter, with evidence of a bank and an external fosse still readable in the cropmark. Tens of thousands of ringforts once existed across Ireland; a great many were levelled during agricultural improvement in the eighteenth and nineteenth centuries, leaving traces like this one as the only record of their existence.