When I started my genealogical quest, I was mostly interested in names and relationships. Soon I learned how important location and historical context were in telling the whole story.

If your ancestors left Ireland during the 1840s, you'll be interested in a fascinating resource which combines data and maps and wonderful graphics. The National Centre for Geocomputation (NCG) has mapped population changes in Ireland from 1841-1851 and provided the data on-line: http://ncg.nuim.ie/content/projects/famine/Index.htm Ireland experienced a dramatic reduction in population during the Potato Famine, but some parts of the country suffered huge declines while other areas gained population.  Using Geographical Information System (GIS), the NGS site shows - by County and Electoral Division - how population changes were impacted by variables such as agricultural practices. It enables you to see what was going on in a particular area during this decade, and it makes (sometimes boring) data spring to life with colorful graphics.

NCG recently launched an additional tool, their Online Historical Atlas Portal:   http://ncg.nuim.ie/redir.php?action=projects/famine/explore.  It gives access to The Irish Famine Population Data Atlas (1841-2002) and the Atlas of Irish Famine Data (1841-1851) .  Amazing! You can slice-and-dice the data to your heart's content!  If you know where your ancestors originated, you can see how population changed where they lived, what crops were grown and even how many habitated/uninhabited houses there were. So much detail! 

If only the database included names...