PDA

View Full Version : How Do I Make a Flat World Map a Globe?



Ashenvale
08-22-2009, 04:15 PM
I've been offered a commission to make a world map for a science fiction setting. The publisher wants a terraformed planet meant to be a replacement for Earth. The art director wants land masses that are overall similar in area to Earth's, and thus similar ocean areas. He wants similar polar ice caps, tropics at the equator, and so on. My guess is he anticipates a similar distance from a similar star, a similar planetary axis tilt, and the familiar climates and weather patterns that ensue. Who knows. He may even want a similar moon and tides.

He asked for a flat map with straight vertical, not curved, longitude lines. He also wants a separete, more detailed continent map, and probably will seek more continent maps hereafter.

This poses a problem. Sci-fi fans, I fear, won't overlook the land-mass distortion arising from a flat map whose polar regions run the full length of a horizontal image. I'll give him the globe map he requests, but I'd prefer to base the continent map on a better projection that takes the spherical nature of the planet into account, so it's not radically distorted.

How do I transform such a horizontal map into a globe map? What program does this best? Do we have a tutorial? My sole expertise is Photoshop. Please help!

Ascension
08-22-2009, 04:50 PM
I never worry too much about distortions on flat maps. Technically they should be skewed the closer you get to the pole (ie lands get widened out so that when pinched they fit on a spherical globe). But on flat maps the lat/long lines run up and down, left and right so I just draw continents to a grid. It's all relative and informative, not technically precise. Maps meant to be wrapped around a sphere in a 3d program get the distortion and for that you could use Fractal Mapper 8 to get a base layout and general shape ideas.

In order to get your distortions correct, if that's what you want to do, then take a look at this thread (http://www.cartographersguild.com/showthread.php?t=2607) as RobA explains how to wrap a flat map around a sphere in Google Earth.

Ashenvale
08-23-2009, 12:52 AM
Thanks Ascension! Great stuff there! I wish the Google Map option allowed creating images with higher resolution and saving those images for practical use. My bet is there's a Photoshop global mapping add-on I haven't found yet.

Until then, what are the proper dimensions for a "flat" (that is, all horizontal longitude lines) global map? Logic suggests 1 high by 3.14 wide to allow for a full circumference at the equator, but most Earth "flat" maps I see are between 1 by 1.6 and 1 by 2. Are they going by a circumference somewhere between the poles and equator, on the assumption that if you go by the full sphere's diameter at the equater that that will distort the regions by the poles too much? I'd hate to build a map at 1 high by 2 wide and then find it cannot stretch appropriately when layed over a sphere.

Ascension
08-23-2009, 01:48 AM
I'm sure that one of the real pros who do that sort of real world mapping can answer this best but here's some facts. The earth is a sphere, with a slight bulge around the equator. That bulge is usually disregarded for our purposes. The circumference around the equator is 24,901 miles and going through the poles it is 24,860 miles. Diameter at the equator is 7,926 and at the poles is 7,900. 3d programs can do a sphere like that but why bother? This isn't a thesis for an astronomy Ph.D. - the difference is 41 miles out of 7,900...or about .005 percent.

Long answer short...3d programs will wrap anything just fine in that the seams will line up but you will get distortions as you get closer to the poles. Most of us use a 1 x 2 scale for flat map skinning to a globe. For reference, here's a map. Notice the dimensions...317 x 635. That's a 1 x 2.

Ashenvale
08-23-2009, 02:43 PM
Excellent. My assumption is that that will cause distortion at the equator, because the ratio of diameter to circumference is less than pi, and great distortion at the poles, of course, but diminish distortion somewhat in the areas between the equator and poles. That seems the best balancing act.

Jykke
08-23-2009, 02:57 PM
Seems to work pretty well (atleast I don't see any major problems). I ran a quick test with the map Ascension posted and learnt something new myself :)

selden
08-25-2009, 02:51 PM
The style of map required by the art director is known as "simple cylindrical", "Cylindrical Equidistant" and "Plate Carré." It is the projection used by most 3D design and display programs for wrapping flat maps around spheres (and oblate spheroids like the Earth). Celestia (http://www.shatters.net/celestia/) uses it, for example.

You didn't mention if the publisher wants ths for a computer game, a tabletop game or a book. For realtime game graphics, it's best to make maps which are a power of two on a side. e.g. 2048x1024. Modern high end graphics cards can handle non-power-of-two images, but older ones can't, thus requiring the maps to be resized by the display software, slowing things down and losing resolution.

Hai-Etlik
09-18-2009, 04:09 AM
Excellent. My assumption is that that will cause distortion at the equator, because the ratio of diameter to circumference is less than pi, and great distortion at the poles, of course, but diminish distortion somewhat in the areas between the equator and poles. That seems the best balancing act.

No, this projection has no distortion at the equator, with the distortion increasing toward the poles, this is a common property of all normal tangental cylindrical projections. What you describe would be a normal secantal cylindrical projection which is rather less common.

Gidde
09-18-2009, 12:51 PM
Flexify is a photoshop plugin that will change one map projection to another. There's a fee involved, but it's well worth it. I've been using it extensively as I try to build a world map for the novel I'm writing, and it's great.

A free alternative is Hugin, which has strengths Flexify doesn't, but it doesn't have as many projections.

RobA
09-18-2009, 02:26 PM
As far as I know, the main reason that the 2:1 ratio is popular with computer applications is because it makes the mapping even, i.e. 360 degrees around the globe and 180 degrees pole to pole. So X and Y with into degrees in a 1:1 fashion.

-Rob A>

Jeff_Wilson63
09-19-2009, 08:39 PM
Somewhere on this site there is a tutorial for a program called Hugin which can create a wide variety of maps in different projections from an equirectangular base map. Hugin is mainly a photo stitcher, but the map features are wonderful.