I can't believe I'm doing this, but I think I'm going to defend Mercator here.
The Mercator projection was indeed originally designed for compass navigation, but the reason it's still used for web mapping is slightly different. The Mercator projection is conformal. What this means is that angles (and hence in some sense shapes) are preserved locally. When we zoom in on a small section of the Mercator projection, we get a reasonably accurate representation of the actual shape of features. This is generally not true for most more fashionable projections, which will stretch and skew things, so they don't always look great when zoomed.
In general with map projections, you have to make a compromise between global properties and local properties. Choosing Mercator means going full-on for local quality, at the expense of the global map being quite distorted. This makes it great for zoomable web maps, because most of the time the global map is just used to find the area you're actually looking for.
Now, you could argue that for a living-room wall, you want something that looks good globally. If it was my wall, I'd agree with you. However, this guy seems to be really interested in local detail. He worries about his four-point fonts becoming blurry, and about having as many small villages marked on the map as possible. If he's interested in that kind of detail, then I think he probably cares far more about local properties than the kind of global properties that would bother me or you.
If I understand correctly, Mercator is the only conformal projection where north is always up, no matter where you zoom in. That makes it nice for online maps. If you relax the "north is up" requirement, there's tons of conformal projections that look nice: http://www.progonos.com/furuti/MapProj/Normal/ProjConf/projC...
I like the "classic Guyou" projection you linked to as well.
But referring back to the OP, notice the grid of books and curios along the entire neighboring wall, and the grid-like pattern of the wood flooring underneath. The Mercator projection seems of a piece with this grid theme in the room.
According to your linked image, one advantage of classic Guyou projection to the writer of the article is that it seems to contain a straight, uninterrupted vertical path through only ocean. He stated that he wanted maximize ocean in his panel cut, but I think he still had to cut through a bit of Africa.
"classic Guyou"... the sizes and shapes of the landmasses are surprisingly realistic
I don't think so at all. Australia is fairly balanced east/west in real life, but on that projection it looks like it's got an eastern tumour. Africa looks like it's got a western tumour. Spain looks like it's the size of the Arabian Peninsula. The British Isles (300k sq km) are the same size as India (3M sq km). It looks horribly distorted compared to a map on a globe.
>The Mercator projection was indeed originally designed for compass navigation, but the reason it's still used for web mapping is slightly different. The Mercator projection is conformal.
Just speculating here, but it's also a big rectangle that is easy on the eyes. Non-rectangular online maps would fit awkwardly in websites. As for Gall-Peters, that map is just irredeemably ugly to me, and I'm ignorant of other rectangular projections that could compete with Mercator.
Yes, absolutely! The Mercator projection isn't the only conformal projection, but it is the only one for which north-south maps to the vertical axis, and east-west to the horizontal axis. That means that it maps the whole world onto a rectangle, which works well both for computers and interior decorating.
As for other rectangular projections, the most common is the equirectangular (or plate carrée), which simply maps (longitude, latitude) to (x, y). This is a pretty common representation for gridded global data.
Gall-Peters is also a conformation projection that maps north-south maps to the vertical axis, and east-west to the horizontal axis. As to online maps one major advantage is the X-Y scale does not get nearly as messed up at multiple zoom levels.
However, online maps alter the projection as you zoom so this is not much of an issue.
Gall-Peters is definitely not conformal. It preserves area, but greatly distorts angles, apart from at the two standard parallels of 45 degrees north and south. This results in the shapes of land masses getting very squished towards the poles (and to a lesser extent, the equator). For an example, look at the shape of Greenland, which appears twice as wide (east-west) as it is tall (north-south), when in reality it's the other way around.
I'm also not aware of any of the main online maps changing projection as you zoom. It seems like that would be more pain than it's worth.
A Mercator projection (ed: is a Conformal map, but) it also greatly distorts both angles and shapes as you approach the poles. The trivial example is to walk a square mile (N,W,S,E) you would expect the opposite sides to be at 45deg angle, but on Mercator the sides get stretched so a square in the real world can have a 10+:1 or even 100:1 side lengths on a Mercator map.
The property they both preserve is points north, south, east, or west of them on a globe are also north, south, east, or west of them in the projection. (Plenty of rectangular projections don't have this property ex: http://geographer-at-large.blogspot.com/2011/08/fun-with-map...)
The issue is interior angels of a triangle on a sphere don't add up to 180 degrees so you literally can't preserve all angles on a projection.
PS: If you actually walk exactly 1 mile north, 1 mile west, 1 mile south, then 1 mile east you don't necessarily end up on exactly the same place on a globe. (It does work if you start half a mile below the equator.)
> as many small villages marked on the map as possible
Based on this image: http://www.dominik-schwarz.net/potpourri/worldmap/images/DSC... the entire continent of Africa looks only slightly larger than Greenland (when in fact it's about 14 times larger), and substantially smaller than Russia (when it is actually ~1.7 times larger).
Greenland has a population of ~60,000. Africa has a population of ~1.1billion.
I think Africa would have more small villages than Greenland (and Northern Russia) combined, yet is afforded less space.
The Mercator projection was indeed originally designed for compass navigation, but the reason it's still used for web mapping is slightly different. The Mercator projection is conformal. What this means is that angles (and hence in some sense shapes) are preserved locally. When we zoom in on a small section of the Mercator projection, we get a reasonably accurate representation of the actual shape of features. This is generally not true for most more fashionable projections, which will stretch and skew things, so they don't always look great when zoomed.
In general with map projections, you have to make a compromise between global properties and local properties. Choosing Mercator means going full-on for local quality, at the expense of the global map being quite distorted. This makes it great for zoomable web maps, because most of the time the global map is just used to find the area you're actually looking for.
Now, you could argue that for a living-room wall, you want something that looks good globally. If it was my wall, I'd agree with you. However, this guy seems to be really interested in local detail. He worries about his four-point fonts becoming blurry, and about having as many small villages marked on the map as possible. If he's interested in that kind of detail, then I think he probably cares far more about local properties than the kind of global properties that would bother me or you.