In Killeennashask, County Mayo, there is a ruined church that the Ordnance Survey recorded faithfully on both its 1838 and 1923 six-inch maps. The graveyard associated with it, however, was left off both editions entirely, as though the cartographers either could not find it or chose not to mark it.

The graveyard's existence, and its significance, was noted by John O'Donovan, the nineteenth-century scholar and topographer who worked on the Ordnance Survey Letters, a remarkable series of field notes compiled during the original mapping of Ireland in the 1830s. O'Donovan recorded in 1838 that the burial ground was known as Cillin na Seasc, and that this name was the very source of the townland's name. A cillin, in Irish tradition, was typically a small unconsecrated burial ground used for unbaptised infants and others excluded from formal churchyard burial, though the name here may simply reflect an older Gaelic place-name tradition rather than that specific function. Whatever its precise character, the site was locally significant enough to lend its name to the surrounding land, which makes its omission from the maps all the more curious. When inspectors attempted to examine the site in 1995, dense overgrowth prevented any proper assessment, leaving its physical condition unrecorded.