For Archopolis, see here.
For Admiralty Center, see here.
There is less on the blog about Tridaig. I think that this is because Poul Anderson tells us less about that city but I might check.
There is a slight lull in posting due to:
Against The Tide Of Years, Chapter Fourteen, describes military maneuvers and has less for me to post about - although I expect to become very interested when Walker and the Nantucketers are back in direct contact and conflict.
When Merseia is unified, Ardaig becomes the planetary capital. Later, it is joined in this role by modern antipodal Tridaig, where most of the government's business is conducted, although Ardaig remains the cultural and artistic center, the location both of the Roidhun's primary residence and of his Grand Council's annual meetings, and also becomes the location of the new Space Navy offices.
-copied from here.
David Falkayn visits, and saves, Mersia long before its unification. Therefore, he visits Ardaig, not Tridaig. Nevertheless, let us reread "Day of Burning" to find out what more can be learned about ancient Ardaig.