I found a site called heywhatsthat.com that is supposed to, (using googlemaps), give you a panoramic view of the mountain peaks you can see from a particular point. It's also supposed to show you the visible field you could see from that point (the view shed). Now I thought this would be useful to map the legendary view across Ireland from the top of the Hill of Tara, I'm not sure it works properly, the site uses raw data from NASA/DEM and as ever its more refined for the US then the rest of the world. I would have expected to see a much larger red area, but maybe it to does give a good indication of the legendary view, and that Tara Hill has sight of a lot more land to the west then the east and that even if built further away that the motorway would have been more visible from Tara to the west. The NRA has said the didn't go west of Tara because of people homes , there was more archaeology there and the motorway would be even more visible from the hill of Tara.Link to Tara panorama.
It also shows contour lines but earthtools.org is better for that.
Tara is the central hill and to the northeast protecting the northern approach is the Rath Lugh promentary fort jutting out into the Gowra river valley in between.