I wonder how many sea boundaries would creep onto land (other than at
their endpoints, i mean) if the sea drops in an ice age. It seems to me
that for most purposes you'd want the boundary to be in the deepest
water: so that future big ships can navigate in either state, and so
that the shallow water (most useful for aquaculture) is neatly divided.

If I were asked to draw a boundary at sea, and if I had good information
about the shape of the seafloor, I'd imagine that the sea has gone dry
and a river flows down from the land boundary; let that river be the sea
boundary. Where that solution is inadequate -- e.g. Bahrain -- drop the
sea until the two landmasses `kiss', and then run rivers down each side
from that saddle point.

(One flaw in this `solution' is that the boundaries of The Gambia, for
example, would likely converge rather close to shore.)

--
Anton Sherwood