I am working out the details behind seatrade.

I am working out the approximate distance from Seyda Neen to:

If I am understanding this I have rough estimates of distance at.

Imperial Waterfront 3100

Bravil 2900

Leyawin 2750

Anvil 3750

That is all in miles.

It's certainly longer to the imperial waterfront than to anvil.

It's 250 miles from Red Mountain to Almelexia according to the first PGE. This distance is consistent with Daggerfalls scale.

http://www.imperial-library.info/maps/maps_tamriel.shtml

First map in there has the scale on the map.

is it consistent with the scale presented in arena's fast travel interface or is that one totally arbitrary?

If we're talking nautically, I'd say it's a little bit shorter than to Anvil. From Seyda Neen to Anvil you have to sail along the entire north coast and half the west. But from Seyda Neen to Imperial Waterfront, I guess you'd have to sail along a part of the north, most of the west, and then double back up the Niben... so it may be equal... It's certainly nearly more economic to ship goods across the Inner Sea, then by land to the Imperial City.