At Corlackan in County Galway, a hachured marking on an Ordnance Survey map, the short radiating lines that cartographers use to indicate a depression or excavation in the ground, drew enough attention to merit a physical visit, only to reveal a sand or gravel pit that had long since been abandoned and absorbed back into the surrounding land.

The marking appeared on the 1931 edition of the OS six-inch map, a series that captured the Irish landscape in considerable detail during the early decades of the state. When someone finally went to look in 1984, more than fifty years after the map was drawn, the pit had been reclaimed, its edges softened, its floor levelled or overgrown, the whole thing returned to something resembling ordinary ground. Sand and gravel pits of this kind were modest industrial features, dug to supply local building and road-making needs, rarely documented beyond the incidental mark they left on a surveyor's sheet. This one had disappeared so thoroughly that only the cartographic ghost of it remained.