The map shows the pattern of settlements by Celts, Saxons, Danes, and Norwegians in the British Isles, as reflected in the place names common to those areas. It’s informative when considering the popular beliefs as to the ethnic makeup of the various regions in Britain and Ireland.
For example, it looks as though the Saxon settlement extended up into the Northeast part of Britain, and those northern regions near Scotland provided a good many of the ‘Ulster plantation’ settlers in Northern Ireland. Obviously (as is already known) those settlers were usually not ‘Celtic’ in origin, as is popularly assumed by many Americans who claim ‘Scots-Irish’ origin.
It also looks as if there was more Danish settlement in Eastern England, which was the place of origin for many New England colonists.
The map is from Isaac Taylor’s ‘Words and Places, or Etymological Illustrations of History, Etymology, and Geography’, London, 1865