Okay, this is what I want to do:

I'm going to make a world map in Excel, by making the cells square,
with blue for sea and green for land.

Then I want to be able to select 2 'ports' eg. NY and Sydney, press a
button, and a macro / optimiser work out the most direct route for a
ship to go between the 2 points.

I'm a professional Excel programmer, have used linear optimisers
before ('What's Best') but haven't yet worked out how to do this, and
was wondering if any of you guys had.

The reason I want to do this: I've got a list of a few hundred "From &
Tos" (some with the option to go via Suez & Panama canals), and I want
to work out eg. all the Journey times, distances, and how long the
ships spend in the middle of an Ocean, out at sea, or in the waters of
which continents. So to do this for each "From & To" I need the map of
the world to have a nice chain of red squares between the 2 ports.

I'm thinking in terms of a linear optimiser, where to start with NY
and Sydney are joined by a 'dumb' square route, and then the optimiser
'smooths' the route into being as short as possible.
Anyone know how I could do that?

TIA
Dz