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Comment by adim86

10 hours ago

I find it shocking that a reputable resource such as this is still displaying the size of Greenland or Africa wrong (Mercator projection) in relation to other land masses in its marketing material and documentation, like here. It just brings doubt to the whole project, which is a shame considering all the time they must have put in. Why show the map that way when majority of its users will never use it for nautical navigation? https://maplibre.org/maplibre-gl-js/docs/examples/display-a-...

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adim86

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dan-robertson  9 hours ago

I’m not sure it’s very useful to rehash an argument with very tenuous relation to the OP here. The normal reason to use the Mercator projection in these situations is (a) it’s what people are used to and (b) it preserves angles so if you zoom in on a street then up will still be north and roads that are at right angles in the real world appear to be at right angles on the map. The latter property is pretty desirable and hard to achieve without doing some weird transition between projections as you zoom. This matters more for Europe (and I suppose parts of British Colombia) where there is a high population density at latitudes that are pretty extreme in much of the world.

I think Apple Maps has a pretty reasonable compromise here of transitioning from a globe to Mercator as you zoom, but this is a less nice UI with a mouse as you need to click to rotate the globe instead of pointing and zooming only. I don’t think there’s anything in this data that would make that unachievable – you just need to reproject the vector data a bit as you zoom out – but it takes some tricky mathematics to get right and so hasn’t been done yet.

  • willtemperley  7 hours ago

    It's an important discussion because it's abundantly clear that almost nobody on this thread has a clue what they're talking about.

    Web Mercator != Mercator.

    I suggest most people on this thread need to go away ask the question "What's the difference between Web Mercator and Mercator".

    • Symbiote  1 hour ago

      For most uses of web maps (navigation on foot, by bicycle or by car) the angles seem to be close enough with Web Mercator, and the map is zoomed in to a small area so there's no concern about the area.

      No-one is zooming out the "Find your nearest Tesco" map to see Greenland.

dzogchen  9 hours ago

It's on our roadmap to support alternate projections, but as you can imagine it's a big project that so far nobody has been willing to pay for to implement unfortunately.

MapLibre GL JS does support globe mode. https://maplibre.org/maplibre-gl-js/docs/examples/display-a-... May we should update our examples to use globe mode when showing examples, especially those that show a world map. We will take that feedback into consideration!

You can use the Equal Earth projection with a plugin: https://equal.bbox.earth/maplibre-americas/

  • readyplayeremma  7 hours ago

    MapLibre's globe mode is both fantastic and performant. Also, it's literally just the one option to change it, and your tile formats/CRS don't need to change either.

    It's the easiest way to escape from web mercator projections with no real downsides that I have discovered yet. Also, there is a built-in control if you want to offer a button to toggle between web mercator view, and globe view, since it's all just rendering changes.

workmandan  10 hours ago

Web Mercator is the standard projection used on the web, if you think the we should use a different projection on the web then that's a completely separate argument

bottled_poe  10 hours ago

Accuracy where it matters is why. Do you have a better suggestion for projecting a sphere onto a rectangle?

  • einpoklum  10 hours ago

    I would not use such strong rhetoric as the GP, but I believe they probably mean we should lean towards using the Gall/Peters projection, which maintains lengths and areas, but not angles.

    (There are of course other projections with other interesting features; or you could take the same projection but center the world differently etc.)

    • ecshafer  8 hours ago

      Why? Why is lengths and areas more important than angles? You have to choose one, its essentially arbitrary. Personally I find it more useful to know what is parallel to what and what is at which angles from what, than some size. We have globes, so we know what the "real size" of Greenland looks like... this has always been a silly argument from the overzealous online looking for right wrongs that don't exist.

      3 replies →

  • willtemperley  9 hours ago

    This comment is inaccurate! Web Mercator causes such large errors in geolocation that the NGA had to issue an advisory about it [1].

    There is a whole science behind map projections and Google ignored it entirely when they created Web Mercator, which was a hack to divide the world into a quad tree. It was vaguely clever and utterly stupid at the same time.

    [1] https://web.archive.org/web/20140607003201/http://earth-info...

    • willtemperley  7 hours ago

      > Accuracy where it matters is why

      Why the downvotes for correcting this laughable statement? Web Mercator is well documented as being extremely inaccurate.

      1 reply →

trgn  9 hours ago

Web mercator is fantastic map. It's well known of course, so very helpful to orient. Plus, its square and easily tile-able, which is good for performance. Shapes of countries are preserved. Plus, the lines are straight, which works great for on screen. Neat and tidy.

Who cares Greenland looks big when zoomed out. "Mercator distorts size" is one of those gis-nerd idee fixes, the first factoid they learn in class, and it overwhelms all thought.

  • mmooss  4 hours ago

    > Who cares Greenland looks big when zoomed out.

    You never know - one day, the geography of Greenland could matter quite a bit to the rest of the world.