Something like https://www.shipmap.org/ could help answer this, but without sounding too trite, it probably depends on where the ship's destination is.

That's a really great visualisation, BTW, thanks.

That's mostly a function of which ports ships travelled between, various choke points (particularly straits and canals), and Great Circle routes.

As an example, shipping traffic between Long Beach (Los Angeles, CA, USA) and Shanghai, China, doesn't head straight out into the Pacific, but hugs the west coast of North America, the southern coast of Alaska, the Aleutian Islands, and threads through the Japanese archipelago, not because today's container ships fear the open ocean and cannot navigate across it, but because that is the shortest route, following a Great Circle from Los Angeles to Shanghai. Similarly, Atlantic traffic between New York and Britain travels significantly further north than one might expect.

WWII saw little US-China traffic, but a great deal of US-UK traffic.

Sea traffic generally would have been concentrated along major supply routes. US-UK, as noted, Japan-Indonesia, and along the Atlantic and Mediterranean coasts of Europe and North Africa. Venezuela was another major oil hub, and Japan was sourcing materials from occupied China and Indonesia.

There's also logistics for attackers: it's militarily advantageous to strike within target-rich environments (where there's a lot of traffic), where the opponent cannot defend or strike back, where traffic tends to be concentrated (straits, islands, port mouths, around islands), within range of a home base or resupply network (the US's western Pacific operations are a solid indicator of just how robust the US logistics chain was, to permit operations over 8,000 mi (13,000 km) from West Coast ports), etc. Hanging out in mid-ocean waiting for the stray target to come into view makes little sense.

Even today, many shipping lanes tend to follow or be shaped by coastlines, see for example:

<https://www.visualcapitalist.com/cp/mapping-shipping-lanes-m...>

That map doesn't do justice to the tremendous traffic from China via Suez to Europe, or the massive amounts of South China Sea traffic, though at least the general routes are evident. It also cuts the US-China route in two by way of the map projection.

I wonder why there’s that “elbow” off the west coast of the US. Is that composed of vessels avoiding the US EEZ or Coast Guard regulation or something?

Which elbow?

There's one which follows the inner Channel Islands passage, and would be used by ships traversing West Coast ports (e.g., between Tijujana, San Diego, Long Beach / Los Angeles, Oakland/Richmond, Seattle, Vancouver).

And there's one further offshore which looks as if it mostly connects the Panama Canal to Vancouver.

I suspect you're referencing the latter, and I'm not sure just what it signifies, though that's in interesting observation, yes.

There are interactive shipping visualisations which show individual ships and their origins / destinations, which might help resolve this.

You are correct, I was referring to that Vancouver-Panama routing.

The more I look at the map, the more I think it does have something to do with some aspect of US jurisdiction - at first I thought the phenomenon was limited to the west coast, but it looks like there’s a hint of it off the east coast as well. And the waters around Hawaii look suspiciously empty (other than traffic that’s Hawaii-bound) compared to the entire rest of the pacific. To my eyes, I don’t see clear evidence of the same phenomenon occurring anywhere else in the world.

Good thought on checking a vessel tracker to see which ships are using that route and whether there are any evident commonalities.

The thing about Hawaii is that there's very little that would pass by there unless it was going to or coming from Hawaii. So the idea that there's traffic around it heading in or out but not much else ... makes sense. There's extraordinarily little traffic across the mid-Pacific otherwise.

(This has strong implications fro the island states of the Pacific as well: they've got great water access ... but nobody goes there. Places such as Pitcairn see very few vessels, similarly for the islands of the South Atlantic.)

I'll see what I can dig up, you're nerd-sniping me.

Agree that Hawaii is (gloriously) remote, but to my eye there still seems to be less shipping in its vicinity on average than there is in similarly remote areas of the Pacific. But I also just noticed I was misinterpreting the scale of the map and had substantially overestimated the breadth of Hawaiian archipelago, so the seeming absence of non-Hawaiian traffic could certainly be a function of, well, being smack in the middle of a giant ocean with not much else around.

That said, another thing I noticed that makes me think could be a regulatorily driven pattern - there’s a quite noticeable void in the map around the Galapagos. I assume that’s some sort of environmental regulation, and vessels either route around (or turn off their transponders) due to that - wondering if there’s a reason to do the same in US waters that doesn’t really seem to hold true anywhere other than the US or the Galapagos.