Thanks for your suggestions. I wish to plot all the DED's for the 1911 census. So, I have tried using the google and the open street map geocoders for all the DEDs in Donegal just to see how I might get on. I am doing this using a Python script. Here is the result:
The first column is the name of the DED. The green columns pertain to Google and the blue Open Street Map.
If I look up "Ardara, Co. Donegal, Ireland" with Google, I get an exact match and I am therefore content with the coordinate: 54.7671456 -8.4092864.
If I look up "Altnapaste, Co. Donegal, Ireland", Google gives me the location: "Meenagrauv, Altnapaste, Co. Donegal, Ireland" which I presume is also, acceptable.
However, I reject "Ballymacool, Co. Donegal, Ireland"'s result of "Ballymacool, Sallaghagrane, Letterkenny, Co. Donegal, Ireland" as I am not sure if there are other Ballymacool's in Donegal. But maybe I shouldn't be so strict... what do you think?
I dont seem to get on as well using the above rules with Open Street Map, but it is interesting to see that I get lots of ED's. For example,
"Three Trees, Co. Donegal, Ireland" gives: "Three Trees, Three Trees ED, Inishowen, County Donegal, Ireland" which my algorithm currently rejects but I should probably accept any match with ED in it I think.
Any suggestions as to how I might proceed?