On a recent trip, I visited Campbell Island, the Southern-most of New Zealand’s extraordinary sub-antarctic islands. A fellow visitor from Ireland pointed out that Campbell is the land mass furthest from home i.e. Campbell Island is the true Irish antipode. I had always assumed (wrongly) that this distinction was held by the eponymous Antipodes Island.
The situation is shown below. Black dots mark the centroids of the small sub-antarctic islands after reflection through the centre of the earth.
Colours show which dot is nearest, using geodesic distances on an ellipsoidal earth. This is just an ordinary Voronoi diagram, expect that the curvature of the Earth is taken into account accurately. (distGeo() function from R‘s geosphere package).
Campbell is the antipode for Ireland and Scotland, while Antipodes Island is antipode for England, Wales and Normandy (except for Anglesea and a sliver of Cumbria).