This kind of site, known as a cropmark, forms when buried ditches or banks cause the vegetation growing over them to ripen at a different rate or reach a different height than the surrounding crop, producing a faint but legible pattern when viewed from above during the right conditions, typically a dry summer.

The enclosure at Coolguerisk is described as univallate, meaning it was defined by a single surrounding ditch or bank rather than the multiple concentric rings that characterise more elaborate defended sites. Its square plan is also notable. Most early Irish enclosures are roughly circular or oval, and a square or rectilinear form is comparatively unusual in the Irish archaeological record, sometimes associated with later prehistoric or early medieval activity, though without excavation it is difficult to assign a confident date to any cropmark site. What the aerial evidence captures is the ghost of a boundary, the faint memory of an organised space that someone once considered worth defining and enclosing.