1. This is a satirical map depicting the American view on the Irish immigration. By the time it was drawn (1860) millions of Irish people had entered the west coast, fleeing from the famine that devastated their country; It shows parts of U.S with a "prediction" implied: If they continue to come, by 1900 they will have taken over the east coast.
2. All the names on the map are Irish related names.
3. It was not easy being Irish on the U.S : religion related issues (Irish Catholicism versus U.S Protestantism), lack of sufficient and good jobs, learning technological skills and foreign prejudice were current challenges they had to face. I think the map might have sent a message to the immigrants that their presence were undesired, in summary.