The mapping of Ireland goes back to Claudius Ptolemaeus (circa 150 AD) and many colourful examples of the early cartographer's art still exist today. However, it was not until the Ordnance Survey established offices here in 1824 that any large-scale mapping of this island started.

According to Ordnance Survey in Ireland: "Born of the need for accurate land measurement for valuation purposes, the Irish Ordnance Survey under Lt Col Colby completed the world's first large-scale mapping of an entire country by 1846. From Fair Head to Mizen Head, and from Howth Head to Slyne Head, every road and track, every stone wall and hedge, every river and stream, every house and barn had been surveyed and mapped."

Early Ordnance Survey surveyors used measuring chains, water levels, limelights and 200lb theodolites as their mapping tools. Limelights were used as markers for angular observations to establish a framework for the survey.

Conditions for the early surveyors in the field were sometimes difficult. While surveying in Donegal a Lieutenant Thomas Drummond, who invented the limelight and hence the stage expression "in the limelight", complained in his diary about the "villainous climate" which blew down his tent and left him writing "from a kind of cave on the lee side of the hill".

"The field surveyors' plots," according to Ordnance Survey in Ireland, "became printed maps by the careful eye and delicate touch of draughtsmen, engravers and printers, using quill pens and Chinese inks and copper plates. "The first six-inch to the mile survey was followed in time by further editions and by larger and smaller-scale maps, accepted by all as authoritative representations of the topography of Ireland.

"But the old production methods have long since gone. Technical developments in the 20th century have transformed the Survey's work, and limelights and chains have given way to electronic distance measuring equipment, satellite positioning systems, aerial photography and computers."

The Ordnance Survey's first mapping of Ireland was done by men from the Royal Engineers with an officer in charge of each field division. Civilians were recruited as well and, at the height of the survey, some 2,100 personnel were employed.

This first survey was directed by Thomas Colby, an officer of the Royal Engineers, and the surveyors started in Ulster during 1825 and worked their way south. A separate department under Richard Griffith demarcated county, barony, parish and townland boundaries - some 60,000 in all.

In addition, a trigonometrical department was set up to provide the surveyors with accurately-fixed control points, and a hill department to represent the ground by hachures or form lines. Later on, a topographical department was established to authenticate collected place-names.

The maps produced by this first "all-Ireland" survey were useful to establish administrative boundaries, and as a basis for a population census and geological surveys. They were also the framework for new Admiralty charts of the coast, railway surveys, harbour works and drainage schemes.

Many early Ordnance Survey maps depicted the site and ground floor plans of buildings, and sometimes indicated the function of the building. They defined the edges of fields, bogs, pasture and woods, and included names of streets and natural features.

As the first surveys were completed and published when Ireland's population was at an historical high - just before the calamitous famine of the 1840s - the maps provide an almost comprehensive guide to population distribution and settlements during that period. All in all, a very important repository of historical record.

Lt Col Colby chose Mountjoy House in the Phoenix Park, which was built by Luke Gardiner as a private residence in 1728, and later used as a cavalry barracks to provide a mounted escort to the Lord Lieutenant who lived nearby, as the headquarters of the Ordnance Survey in Ireland.

According to Leonard Hynes of Ordnance Survey Ireland: "The late 1840s saw the introduction of new large-scale surveys of towns, which were published. Levels were added to the six-inch sheets. The survey continued to expand its publications in the 1850s and 1860s with the introduction of the one-inch map. Approval was eventually given in 1887 for a 1:2,500 survey of Ireland. This survey was completed in 1913.

"The early 1900s also saw the introduction of maps in colour at one inch to one mile, one-quarter inch to one mile and a half inch to a mile. The Ordnance Survey continued to revise the existing mapping until 1964. A committee was then set up to examine the future mapping needs of the country."

During the second World War, a large part of Britain's repository of maps and land surveys was destroyed in a Southampton office. As this State remained neutral during that conflict, a terrific bank of maps has survived at the Ordnance Survey's offices in the Phoenix Park. A significant part of this repository is now in the hands of the National Museum of Ireland for preservation.


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