Ireland has a dramatic and unusual population history, with overall population declining dramatically from 8.2 million to 6.5 million between 1841 and 1851 and then declining gradually and almost continuously to 4.5 million in 1961.
The quote is from an article  in Irish Geography which describes a splendid resource combining various data to chart this “dramatic and unusual population history”. The resource in question is the Irish Population Change Atlas, an interactive, online resource detailing 160 years of Irish population history through which population change can be explored and researched.
The article discusses the collection of the data and how it is made available online by using 16 census returns from 1841-2002 and mapping these onto the electoral districts of Ireland. These districts (3432 in total and based on the 1851 Electoral Division boundaries) have remained largely stable over the time period and where they have changed the team has made compensations.
The availability of such population data at a consistent set of boundaries means that researchers can now examine population change for the entire island. The article also gives a statistical analysis of population trends for various time periods. Furthermore, other avenues of possible research are suggested such as the impact of roads, urbanisation and rural migration. The intuitive (i.e. press a button) download data option will help in this research (data is downloaded into an excel document). There also seems to be a facility to map the changes onto different maps – a menu offers “Satellite”, “Terrain”, and “Hybrid”, however I could not get these maps to display. There is also an “Export as image” download but I could not get this to work either.
The Atlas, based at the National Centre for Geocomputation at NUI Maynooth, cleverly charts population change by map, county, place names, graphs and a timeline. It is a testament to the ingenuity of the team and software that so much information is displayed in an easily digestible and easy to use resource. Users must have Adobe Flash Player 9.0 or above to use the site.
 Kelly, M. and Fotheringham, Stewart A. The online atlas of Irish population change 1841–2002: A new resource for analysing national trends and local variations in Irish population dynamics. Irish Geography, vol. 44: 2-3, 2011