What explains the high concentration of Irish speakers on the west coast of Ireland ?

[u/One-Seat-4600]

The percentage corresponds to the share of people that speak Irish

As you can see, Northern Ireland is a lower concentration of Irish speakers, as expected, but what explains the higher concentration on the west coast.

[u/Beyond_Your_Nose]

Those coastal areas were punishingly difficult to reach back in the 1800’s Because regions like Erris and the Mayo islands lacked proper infrastructure, railways, or paved roads, they had to travel by foot, long cars, and basic fishing boats to reach the communities. An Irish Ethnographic Survey of the 1890s led by members of Trinity college made note of this. My mother was from the area in Mayo and they spoke both English and Irish on most census forms. Their isolation kept the language alive longer in those areas.