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Comment by reliablereason | Hacker News Reader

That is a terrible use of the Mercator projection.

The extra distance around Africa looks comparatively small on the Mercator projection.

This is arguably where mercator shines. Note that the paths are straight lines. Otherwise you'd be scratching your head as to why they're taking long curved routes instead of straight paths.

And the distance is going to be distorted no matter what.

Good points. Since there are so many projections I thought there would be one for distances but the equidistant projections only work for specific points of origin. https://en.wikipedia.org/wiki/Map_projection#Equidistant

Except the shortest distance between two points on the surface of a sphere is a geodesic, not a rhumb line. So a straight line on a Mercator projection (rhumb line) is not a "straight" line on the surface of the planet, and if I see a long straight line, I'm asking "why aren't they taking the shortest path?"

Straight lines on mercator are a constant bearing which is the most simple way to navigate.

Do ships still use rhumb lines? I'd have thought that modern technology was good enough to guide them along geodesics.

Ships often follow shipping lanes. Many shipping lanes are deliberately rhumb lines rather than great circle paths.

But the Mercator projection doesn't show shortest-paths as straight lines unless they're north-south or the equator.

Gnomonic projection shows great circles as straight lines: https://en.wikipedia.org/wiki/Gnomonic_projection

Good thing Ryan's tweet is about the ratio of the number of ships diverted from their normal route (orange dots vs black dots), not about the absolute distance. "Look at how much orange there is". It's implied (and well known) that the route around the tip of Africa is longer (in both time and distance), it doesn't matter how much longer to make the point that the previous route is now considered riskier and many are chosing an alternative.

My understanding is that it's about 20% longer for ships coming from Asia. That means a 20% reduction in annual capacity for those ships/shipping companies, which is pretty massive.

> My understanding is that it's about 20% longer for ships coming from Asia. That means a 20% reduction in annual capacity for those ships/shipping companies, which is pretty massive.

Not to be a total nit but thought it worth pointing out that 20% longer transit time for a particular transit route likely does not directly translate to a 20% reduction in annual capacity as port delays for on/offloading and other factors also determine annual capacity and they can be extremely variable as well.

Fair enough, it was just meant to connect the dots on how a longer trip also means lower capacity.

> The extra distance around Africa looks comparatively small on the Mercator projection.

Compared to what? I.e. what projection or approach would you choose instead of Mercator?

A projection that is better at showing the comparative difference in length between going through the Suez canal vs going around.

The mercator makes Africa look comparatively small on the y-axis which is a problem if you are trying to visualise the size of Africa and the time it takes to go around the continent.

If i visually compare the distance on the mercator and an equal area projection is looks to make the trip about 20% shorter on mercator (compared to the apparent visual distance going through Suez). Non of the projections will be 100% accurate but the mercator is less accurate for this specific case.

> The mercator makes Africa look comparatively small on the y-axis which is a problem if you are trying to visualise the size of Africa and the time it takes to go around the continent.

LOL.

The Suez canal is at ~30°N, while Cape Town is ~35°S. If anything the Mercator projection is exaggerating the visual distance of going around.

Hating on Mercator is just pavlovian concern trolling at this point (it's the first thing people learn in their GIS classes, whatever). People are so obsessed with conservation of area, it's cringey, Freud would have something to say about that. Maps should always neatly establish a frame of reference. Unless you need to actually take out a ruler and measure a thingie of of it, projections don't matter all that much. The mercator map is an excellent world map: land masses nicely proportioned, straight reference lines that don't clutter, north is up thank god, no weird bulges, just rectangular, you know, like a page in a book or a website. It's just a really good world map. The haters are wrong 90% of the time.

Considering that the discussion is about shipping in the southern hemisphere then maybe choose one of the many different map projections that better represent that part of the world.

such as?

Many of you will be well aware that you can't have a distance-preserving "map", that is a projection from the globe to a segment to of the plane where the length of an arbitrary path is preserved. Hence you can't measure real-world distances using string and a paper map.

That said you can preserve distance in special cases, for example any two chosen points. For example you can go to https://www.jasondavies.com/maps/two-point-equidistant/ and put your points at the Suez Canal and the Cape of Good Hope. While that still won't let you measure wiggly ship routes along the coast, it does a better job than Mercator.

Failing that you can use Gall-Peters which does a better job of conveying the vastness of Africa, since it's area preserving.

> Hence you can't measure real-world distances using string and a paper map.

You very much can. The scale of longitude and latitude is just not the same so you need to do Pythagoras (usually by approximation rules).

There are usually lines to allow for that.

If you only use rigid string and sail in strange curves that map to straight lines in 2d then that's true. Or maybe by "do Pythagoras" you meant to calculate the metric tensor for your projection and integrate that along your shipping route?

Is measuring distances in Google Earth misleading? Why bother with ancient flat maps?

The measuring tool is accurate. The way it appears on your screen is always misleading in some way, because your screen is flat.

They actually curve the line of the measuring tool so that it follows the geodesic.

Ideal would be an embedded gif (or even interactive widget) of a 3D globe rotating, with the lines drawn on it, but obviously that's a lot more work.

A radical idea would be making the Northeast South America the Western world distribution center via the Cape -- a great circle route from Indonesia. Export to the rest of the West from there, while letting the ships go quickly back-and-forth. A bold and probably a little more expensive solution in the beginning, but far safer. That would diminish the Strategic value of the Red Sea, as far as the world commerce goes.

I ran some measurements, this would replace the Malacca Rotterdam 14,000km route with a 22,000km long route at least, increasing costs by 50%. Not realistic IMO

Isn't this backwards? The equatorial regions including the Red Sea are compressed by Mercator while the high latitudes around the Cape are stretched.

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