
Why Mercator for the Web? - hokkos
https://www.mapthematics.com/forums/viewtopic.php?f=8&t=251
======
aspir
I'd love to see a mapping service with dynamic projection functionality based
on zoom and window view. The concept of one fixed projection doesn't account
for the nature of digital mapping today.

~~~
magicalist
Yes, I'd love a major mapping service to consider something like
[http://cartography.oregonstate.edu/demos/AdaptiveCompositeMa...](http://cartography.oregonstate.edu/demos/AdaptiveCompositeMapProjections/)

We now have maps that resemble nothing like any paper map before. There's no
reason at all they have to be like zooming closer to the biggest paper map
ever made.

(Web) Mercator is almost certainly the right choice for the things most people
use maps for: local directions, routing etc. Minimal distortion on that scale.
If you look at the "Projection Diagram" on that page, Mercator is only used
for the highest zoom levels, however. Above that it's adaptive based on both
zoom and latitude.

~~~
kuschku
By the way, a comparison between Google Maps in satellite view and in map
view: [http://imgur.com/a/GXczm](http://imgur.com/a/GXczm)

(satellite view uses a projection on a sphere, and then renders the sphere
from the users current viewpoint)

------
Illniyar
"Yet when you look objectively at the impact a map projection has on the
beliefs and world view of the general populace, you really don’t come up with
much. Maps are only a tiny part of most people’s lives. They’re exposed to
many projections anyway—as they should be. They take cues from a map in many
ways, not just relative sizes. And mostly, they really don’t care."

Well, personally, I've never been exposed to other projections until 28 years
of age and that was only because I happened upon an article about how wrong
mercator projection is on Hacker News.

While it really is a tiny part of my life and I don't really care, the
realization that Africa is huge and almost three times bigger then Europe and
that Greenland is tiny is something I consider an important thing to know -
and probably changes some of my views on things (for instance I never quite
understood how Africa has so many countries - which if you triple it's size,
it becomes much clearer).

~~~
daanstrebe
"Well, personally, I've never been exposed to other projections until 28
years…"

That is vanishingly unlikely. These are projections you have practically
certainly seen:
[https://www.mapthematics.com/ProjectionsList.php?Projection=...](https://www.mapthematics.com/ProjectionsList.php?Projection=84#Robinson)
[https://www.mapthematics.com/ProjectionsList.php?Projection=...](https://www.mapthematics.com/ProjectionsList.php?Projection=189#Winkel%20tripel)
[https://www.mapthematics.com/ProjectionsList.php?Projection=...](https://www.mapthematics.com/ProjectionsList.php?Projection=69#Mollweide)
[https://www.mapthematics.com/ProjectionsList.php?Projection=...](https://www.mapthematics.com/ProjectionsList.php?Projection=159#orthographic)

And many others. Also, people often mistake any rectangular projection for
Mercator. I have even seen this happen in academic literature.

------
mrgriscom
Hey, some of us like the extreme distortion of the Mercator projection!

[http://mrgris.com/projects/merc-extreme/](http://mrgris.com/projects/merc-
extreme/)

It is interesting how WebGL is enabling the use of dynamic re-projection and
making the old web Mercator tile pyramid obsolete. Also kind of sad, though;
the 'slippy map' heralded a new age of map openness, interoperability, and
opportunities for remixing. I will be very sad to see that go...

~~~
vacri
How good are you at identifying country shapes with the mercator distortion?

[http://bramus.github.io/mercator-puzzle-
redux/](http://bramus.github.io/mercator-puzzle-redux/)

Might need to zoom in a little. The original was a little easier, but didn't
randomise the country set - the redux version picks lots of tiny globs that
are hard to identify at scale

[https://gmaps-
samples.googlecode.com/svn/trunk/poly/puzzledr...](https://gmaps-
samples.googlecode.com/svn/trunk/poly/puzzledrag.html)

------
robotcookies
Do people really complain because google maps uses Mercator (or a similar)
projection? My understanding was that the complaint was when Mercator is used
for wall maps like in the classroom. When you show the whole world using it,
the sizes of the continents are way off proportion.

On a zoomed in scale like when showing streets or smaller areas, it doesn't
matter.

~~~
jacobolus
The problem is that Google Maps has become a very convenient always available
source for maps, and the brand is highly trusted. Moreover, many other online
mapping services have adopted the same projection.

Students (or whoever else) who might have previously gone to look up a region
of the world on a globe, large paper map, or atlas are now turning to sites
like Google Maps instead. The market for high quality paper maps has fallen
quite a bit as more convenient online maps become the go-to source for
answering all sorts of geographic questions.

Moreover, Mercator maps are turning up as the basis for many other tools. For
instance, several online map collections have started georeferencing and
reprojecting historical maps onto a Mercator projection, saving them as raster
tiles, and allowing visitors to pan and zoom around on those reprojected maps,
Google-Maps style. Instead of looking at various original maps with region-
specific projections, now the viewer is getting more and more exposure to just
Mercator maps.

If you look around the web, there are many examples of good maps with
reasonable projections, but there are also many many examples of people using
the Mercator projection in wholly inappropriate contexts. For example, I see
Mercator choropleths of US statistical data quite frequently, which should be
using something like an Albers equal-area conic projection instead.
([http://bl.ocks.org/mbostock/3734308](http://bl.ocks.org/mbostock/3734308))

On the bright side, work like the D3 guys (Mike Bostock & Jason Davies) and
others have been doing has made it easier than ever to construct nice web maps
in all sorts of projections, without shelling out big bucks for fancy GIS
software.

[http://www.jasondavies.com/maps/](http://www.jasondavies.com/maps/)

[https://github.com/d3/d3-geo-projection/](https://github.com/d3/d3-geo-
projection/)

~~~
emn13
What's the problem with a mercator choropeth? Assuming scaling by area (if
necessary) is done on the true area (not the distorted area visible), I can't
see any obvious issues - am I missing something?

~~~
daanstrebe
It depends on the extent of the map. For local areas, what you suggest is just
fine. At the scale of a continent, it’s problematic, and gets more and more
problematic as you zoom out.

------
fennecfoxen
Summary: It's about the only conformal map out there where "north" is always
up. (Conformal: when you zoom in on it, the map that you see has the right
shapes and so makes sense locally, and is not terribly distorted.) So you can
pan and zoom to your heart's content.

~~~
saurik
That is the first over-two-thirds of the article, which is an argument for
Mercator. Web Mercator is not conformal, which is admitted in the last part of
the document. I personally find the final argument for Web Mercator to be a
bunch of hand waving that seems to use "complexity" in inconsistent ways,
ignoring that having data that is actually accurate and based on a consistent
formula is "less complex" even if it requires a small amount of extra
trigonometry (and I'm not even certain that that is really true, though I have
not had a chance to finish all of the reading I have on my todo list for map
projections, Web Mercator in particular; see URL).

[http://cegis.usgs.gov/projection/pdf/Battersby_Implications%...](http://cegis.usgs.gov/projection/pdf/Battersby_Implications%20of%20Web%20Mecator%20and%20Its%20Use%20in%20Online%20Mapping.pdf)

~~~
jacobolus
It’s kind of stupid to use “Google Mercator” instead of a conformal
cylindrical projection of an ellipsoid
[http://en.wikipedia.org/wiki/Mercator_projection#Generalizat...](http://en.wikipedia.org/wiki/Mercator_projection#Generalization_to_the_ellipsoid)

However, the difference between that and Google Mercator is in practice pretty
slight, since the flattening of the WGS84 ellipsoid is only about 1 part in
300. It’s not really that big a deal for most uses, IMO. Anyone with a use
case where it matters can pick a different projection and either source data
elsewhere or reproject the data from Google Maps or whatever similar source.
If people are using Google Maps (or similar) data in inappropriate contexts,
they should stop doing that.

The bigger problem is using a Mercator projection at all for small-scale
(zoomed out) views of the map in contexts like a convenient online map viewer
where less savvy viewers are likely to be mislead by the scale distortion, and
get little benefit from having straight rhumb lines.

------
krick
That's pretty long post about nothing. It starts with a lie ("As you may know,
Google Maps uses the Mercator projection."), which is admitted in the very end
of the post, making previous musings somewhat misdirected.

The most obvious reason to use web-mercator is it is easily computed. Probably
the _real_ reason to use it now is that people are used to it. Most google
maps (or even OSM) users probably don't even suspect there's something wrong
with that map, and don't imagine there are other projections. The only people
who complain is a bunch of cartographers, and who cares about them, right?

So I don't expect something is gonna change and don't really know if it is
easy enough to provide alternative projections for OSM. For google maps at
least there's google earth.

For me, as a user, it is inconvenient. I almost never care for north to be
exactly on top. I use maps on large scale to answer questions like "hm, so
where is that Sahara desert? How large is 9,400,000 square kilometres? How far
is the distance between these two airports? What is Cambodia?" To answer these
questions web-mercator is nearly the worst projection possible.

On small scale I don't even expect the map to be precise, I just need it to
tell me where should I turn to get where I need. So on small scale web-
mercator isn't harmful for me, but most other projections wouldn't be either.

Personally I like Kavrayskiy VII projection¹. The only thing I dislike about
it is the fact it make Antarctica to look huge. I wonder why it isn't more
popular, really.

[1] -
[http://en.wikipedia.org/wiki/Kavrayskiy_VII_projection](http://en.wikipedia.org/wiki/Kavrayskiy_VII_projection)

~~~
nemo
"It starts with a lie"

Web Mercator is a Mercator projection, so it's not a lie, just slightly
imprecise.

"which is admitted in the very end of the post"

The post discusses Web Mercator in the second sentence.

"The most obvious reason to use web-mercator is it is easily computed."

Which the article discusses.

"For me, as a user, it is inconvenient. I almost never care for north to be
exactly on top."

Google maps has a lot of users with various use cases. For uses involving
directions, conformal maps are better, and the maps are heavily used for that.
All engineering decisions are compromises, Google's compromises apparently
were the best for their expected use cases.

------
cozzyd
Those of us with experiments in Antarctica really dislike Google's Mercator
projection.

~~~
daanstrebe
« laugh » No kidding…

------
filereaper
The West Wing did a really good clip on what's wrong with the Mercator
Projection.

[https://www.youtube.com/watch?v=vVX-
PrBRtTY](https://www.youtube.com/watch?v=vVX-PrBRtTY)

