This map shows the population Densities in 1841 and 1851, showing the number of persons per 100 acres. In 1841 there was very high levels of population density in the area encircling Lough Neagh and sweeping in a large crescent south-westwards as far as the borders of south Leitrim, north Longford and north Roscommon. 

It might seem surprising that the uplands of Donegal, west Mayo, much of Connemara, south Kerry, Wicklow Mountains and smaller pockets in the east Leinster had very low densities per 100 acres. 

The mountainous areas, however, were relatively newly settled in the 1840s, and represent the push into remote upland areas as a result of an increasing population and the fact that the rocky soil could support the proliferating potato drills. 

While some parts of the country are more resilient than others - especially the high-density belt around Lough Neagh - it is clear from the 1851 map that there is a significant reduction in population densities across all parts of the country. 

While south-eastern Ulster and North Leinster shows significant decline brought on by the demise of cottage industries, it is in Munster and Connacht where the impact of the Famine is felt most with the sharp decline in the cottier and labouring classes. 

A striking feature of the 1851 map is the high density in some coastal districts, particularly in South Donegal and West Cork which suggest that survival rates were higher where the coast was low-lying and accessible.