The action takes place in late August 1833 at a hedge-school in the townland of Baile Beag an Irish-speaking community in County Donegal. In a nearby field camps a recently arrived detachment of the Royal Engineers making the first Ordnance Survey. For the purposes of cartography the local Gaelic place names have to be recorded & rendered into English. In examining the effects of this operation on the lives of a small group Brian Friel skillfully reveals the far-reaching personal & cultural effects of an action which is at first sight purely administrative.