the first Director of the Ordnance Survey of Ireland, made a study of the ancient land divisions of Ireland and summarised the traditional hierarchy of land divisions thus: 10 acres – 1 Gneeve; 2 Gneeves – 1 Sessiagh; 3 Sessiaghs – 1 Tate or Ballyboe; 2 Ballyboes – 1 Ploughland, Seisreagh or Carrow; 4 Ploughlands – 1 Ballybetagh, or Townland; 30 Ballybetaghs – Triocha Céad or Barony. This hierarchy was not applied uniformly across Ireland. For example, a ballybetagh or townland could contain more or less than four ploughlands. Further confusion arises when it is taken into account that, while Larcom used the general term "acres" in his summary, terms such as "great acres", "large acres" and "small acres" were also used in records. Writing in 1846, Larcom remarked that the "large" and "small" acres had no fixed ratio between them, and that there were various other kinds of acre in use in Ireland, including the Irish acre, the English acre, the Cunningham acre, the plantation acre and the statute acre. The Ordnance Survey maps used the statute acre measurement. The quality and situation of the land affected the size of these acres. The Cunningham acre is given as intermediate between the Irish and English acres. Many of these land division terms have been preserved in the names of modern townlands. For example, the term "cartron" in both its English and Irish forms has been preserved in the townland names of Carrowmeer, Cartron and Carrowvere, while the term "sessiagh" survives in the names Shesia, Sheshodonell, Sheshymore and Shessiv. The terms "ballyboe" and "ballybetagh" tend to be preserved in the truncated form of "bally" as a prefix for some townland names, such as Ballymacarattybeg near Poyntzpass, County Down. Less well-known land division terms may be found in other townland names such as Coogulla (, "the Ulster fifth"), Treanmanagh (, "the third middle") and Dehomade (, "the tenth part"). A problem with the term "bally" in some townland names is that it can be difficult to distinguish between the Irish terms baile meaning "townland" and béal átha meaning "approach to a ford". An example of the latter is Ballyshannon, County Donegal, which is derived from Béal Átha Seanaidh. Size and value The average area of a townland is about , but they vary widely in size. William Reeves's 1861 survey states that the smallest was Old Church Yard, near Carrickmore, in the