Continuation of my Q about the SW corner of the Bite: (2) If this region belonged to the Tullys, would it be a good location for a port town in the context of your Economic Development Plan for the Riverlands? (3) If it is House Arryn’s *cough!, would it be worth the trouble to get your hands on the lands?

1. I’m assuming you mean that strip of land along the coast immediately south of the Sisters, and not the part of the Riverlands along the kingsroad (which the Valemen tried to capture during the reign of Rolland II Arryn, who was defeated and later beheaded by Tristifer V Mudd). 

It’s a bit tricky, because that land doesn’t always exist, depending on the map. (Incidentally, the World of Ice and Fire map of the Vale is completely rubbish – somehow putting the Mountains of the Moon smack-dab on top of the Vale proper, to the east of the Bloody Gate) Some of the various book maps, for example, as well as Tear’s fan map (which GRRM endorsed pre-Lands of Ice and Fire), show the mountains coming up right to the coast as opposed to having this decent stretch of level ground.  

Now, I don’t think it’s that impossible for this land (if it exists) to Arryn rather than Tully – for one thing, it’s substantially to the east of the Mountains of the Moon, which seems to have been the historical boundary between the Riverlands and the Vale. It’s also really close to the Sisters and the northernmost Fingers, suggesting that historically those lands would have been in the orbit of either the Sunderlands or the Coldwaters or the Belmores or the Lynderlys or the Corbrays.

2. As a port…eh. It’s got a couple problems in that White Harbor and the Sisters are already-established competitors really close by, so you’re going to struggle to get off the ground. Exporting your goods into the Vale itself is going to either involve sailing all the way around the coast, in which case why not cut out the middleman and sell to Gulltown directly, or an incredibly expensive and risky mountain portage. If instead you want to export to the south or west, you’re going to run into some pretty steep rent-seeking from the Riverlords (especially the Freys if you want to access Seagard’s port), and it’s not really that much of a time saving compared to just going to White Harbor and taking the Kingsroad all the way down. 

3. It honestly depends on how productive these potentially non-existent lands are. The Riverlands aren’t exactly wanting for farmland, and they have easier ways to access the Narrow Sea through Maidenpool and Saltpans and the like. And it would be very hard to hang onto them, because they could be pretty easily cut off by a force landing from the Sisters.