7 replies to this topic

[Sakura]

Hi am doing an assignment and would really appreciate some help and opinions regarding map projectioin.

If you had to select a map projection to fairly display all earths countries, which would you choose and importantly why?

[Charles Syrett]

We need more information in order to help you. What exactly do you mean by "fairly display"?

Assuming that you mean that you want the relative physical areas of the countries to be intact, then you need an equal-area projection. Such projections, however, tend to introduce distortions in shape -- and then how do you choose which part of the world will be distorted?

On a side note -- the Mercator projection has often been criticized for its area distortions (showing northern latitude countries much larger, proportionally, than tropical countries). Mercator actually fell into a lot of disfavour in the late 20th century for its "political incorrectness". In recent years, we've seen "Mercator's Revenge", since this is the projection used by Google and Bing, and therefore arguably the most-viewed projection nowadays.

Charles Syrett
Map Graphics
http://www.mapgraphics.com

Hi am doing an assignment and would really appreciate some help and opinions regarding map projectioin.

If you had to select a map projection to fairly display all earths countries, which would you choose and importantly why?

[Sakura]

Hi there, thank you for replying. "fairly" is open to interpretation.

So far my ideas are:
Robinson Map Projection, neither equal-area or angle-preserving - a compromise. Its also visually appealing.
The mention of the Mercator map lead me to...
Peters Map Projection, minimal area distortion. Some think that its a fairer view of the world compared to the Mercator.

I'm just starting out, but so far I understand that all map projections have their distortions/advantages, I'd like to know if you have a preference and why?

[Hans van der Maarel]

I would not recommend Peters (or Gall-Peters if you want to be really correct). Partly because of all the controversy it generated but mostly because I don't like the way it distorts the world.

Maybe you can give Flexprojector a try. It'll show you what effect changes in the parameters have for angular/scale/area distortions.

[frax]

My preference is Wagner VII (also know as Hammer-Wagner), which is an equal-area projection with decent distortions (which I got recommended by Daan Strebe and Fritz Kessler at a NACIS dinner two years back). The downhand is that the polar areas gets budged a bit, and instead of an ellipse shape of the globe you get a sort-of-batman-logo shape (which I find a bit cool). This projection is not supported by e.g. ArcGIS. You can see a map I created in this projection here.

If I can't use that, I use Winkel Tripel (which is not equal-area, but a decent compromise), or Goode's Interrupted Homolosine. I also find more esoteric interrupted projections interesting, like Oblique Hotine Mercator and the Fuller projection.

[frax]

Oh, and I would stay away from Gall-Peters - it is equal-area, but it has heavy (unsightly) distortion. Part of the hype around it is that it has been presented as the only equal-area projection, which is not true. Compare that to Wagner VII, and I find the latter preserves the shape better.

[M.Denil]

There are a number of good equal area projections; the biggest decisions you have to make are the outer shape and proportions of the map, and where exactly you want to have the most shape distortion. ALL equal area projections distort shape, so the question is; where, and how much?

If you want a rectangular map, with square corners (cylindrical):
A Lamber't equal area cylindrical makes a long skinny map, with the poles streched east and west and compresses north and south. It is only true shape is at the equator. The Gall-Peters uses a standard paralel of 45° (which runs through Nova Scotia!), so it's shapes are only correct along those lines (45° north and south). Higher latitudes are streched east and west and lower latitudes are streched north and south. I usually go for a Behrmann Projection (if I need a rectangular projection). It uses 30° standard parallels, and thus is a compromise between the extreams of Lambert and Gall. It is also supported by ArcMap.

If you want round ends on you map (pseudo-cylindrical):
I would NOT choose a Robinson. It was composed by old Robinson so it "looked right", at least to Dr. Robinson. There is, however, nothing about it that IS right.
I have long been partial to the Eckert IV (or Eckert 4). It equal area, shows the tropics and the high latitudes well, is supported by ArcMap (but not by AV3), and still "looks right": righter than the Robinson (if you ask me).

There are other equal area projections: for instance, Lambert invented a nice azimuthal version. It makes a round map with LOTS of shape distortion on the far side of the earth from you map center, but sometimes that is okay too....


M.Denil

[natcase]

I'm a fan of interrupted projections like the interrupted Goode's Homolosine, at least when you are focused on land areas. Playing with the triangular pieces of Buckminster Fuller's Dymaxion projection can be a great way to explore what's next to what on a flat surface. And it makes the point about spheres projected on to flat spaces tactilely.