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#1
frax

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Hiya,

I was just looking at some thematic maps I prepared some time ago, with things about the oceans. I used the Wagner VII projection for this (an equal area projection with a decent trade-off in deformation, if you ask me), and I use 10 deg E for the center of the map, to avoid the far end of Russia being cut-off.

Now, when I look at it now, I wonder why I didn't choose another central meridian, one to display the oceans better, and I started to experiment a bit. An interesting thing though, is when you make maps over marine natural resources, is that most of the action is close to land, and on the continental shelves, so that is the pieces you want you to display clearly. There is not that much happening in the center of the pacific.

So if I do this again, which central meridian do you think I should choose? My first thought was to have 20E in the "wrap" and -160 in the center, which would display all oceans clearly, it is just that with that view, the coasts of Europe/Africa gets a lot of deformation...

World map of ocean productivity
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Hugo Ahlenius
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#2
Hans van der Maarel

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So if I do this again, which central meridian do you think I should choose? My first thought was to have 20E in the "wrap" and -160 in the center, which would display all oceans clearly, it is just that with that view, the coasts of Europe/Africa gets a lot of deformation...


Depends on what you want to map. Using -160 would put the Mediterranean right in the wrap. If you have a lot of stuff going on there, that's probably not such a good idea. If you shift the wrap further east, you end up with the Red Sea, Black Sea, Caspian Sea and/or Persian Gulf being divided. If you shift to the west, you're cutting through the North Sea and Atlantic Ocean.

A central meridian of 150 seems to work okay. The only major landmass being cut up are Greenland and Antarctica, with the wrap running down the Atlantic ocean. Distortions aren't too bad.

Attached File  2004_07_WagnerVI_150_Flex.jpg   144.76KB   30 downloads
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#3
frax

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Hmmm... It's tricky. Maybe one should look again at something at the Goode's interrupted homolosine for oceans as well. I don't mind land areas being cut up, but I have to think about this some more...
Hugo Ahlenius
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#4
Hans van der Maarel

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Hmmm... It's tricky. Maybe one should look again at something at the Goode's interrupted homolosine for oceans as well. I don't mind land areas being cut up, but I have to think about this some more...


Goode's is a good one too, but I don't know of any software that lets you set the interruptions manually. Geocart perhaps... I spoke to daan Strebe at NACIS and he said the new version was in the final stages of testing.
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#5
Nick H

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Hmmm... It's tricky. Maybe one should look again at something at the Goode's interrupted homolosine for oceans as well. I don't mind land areas being cut up, but I have to think about this some more...


For me at least it's difficult to see how re-jigging might improve the original, which is a map with a very clear message presented very clearly. In my view the message is the essence of a map like this and it is the message that must be preserved at all costs, even if this entails sacrificing prettiness.

If it ain't broke...

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#6
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Nick - for presenting the coastal/continental shelves area as in the original map, that projection was probably the best - breaking in the Pacific where not that much of the action is happening. If one would do a map communicating important issues in the high seas, it would be different.

It would also be interesting to experiment with maps that duplicate a slice of area for the break here maybe - there was a topic some time ago about someone preparing a map and trying to duplicate a slice close to the 'other side of the World' break in a Van der Grinten projection map.
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#7
Charles Syrett

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Here are some screenshots of the current version of Geocart. When you pick Goode's, you can select interrupts from a diagram (see Interrupts.png). The top middle is the default. I tried the one directly below it (Goode1.png) and the one in the middle right (Goode2.png). You can also manually change the center of the projection, which I did for Goode3.png. B)

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Hmmm... It's tricky. Maybe one should look again at something at the Goode's interrupted homolosine for oceans as well. I don't mind land areas being cut up, but I have to think about this some more...


Goode's is a good one too, but I don't know of any software that lets you set the interruptions manually. Geocart perhaps... I spoke to daan Strebe at NACIS and he said the new version was in the final stages of testing.

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When I first looked at the larger version of this map I was struck immediately by the zone of elevated biomass stretching from the north-west coast of Europe over to Canada. Bristol fishermen are said to have been working the great banks off the coast of Labrador and Newfoundland for years before Columbus arrived on the scene and I suspect they wouldn't have been the kind of people who would set out into the cruel Western Ocean on the off-chance of stumbling on something worthwhile. But looking at the map, it made me wonder if what they did was to follow the fish.

Doubtless this is all nonsense, but the point is that the map made me think.

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#9
Fran├žois Goulet

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Hmmm... It's tricky. Maybe one should look again at something at the Goode's interrupted homolosine for oceans as well. I don't mind land areas being cut up, but I have to think about this some more...


Goode's is a good one too, but I don't know of any software that lets you set the interruptions manually. Geocart perhaps... I spoke to daan Strebe at NACIS and he said the new version was in the final stages of testing.


ArcGIS has it. For land and ocean... It cames with 9.2 I think... finally!

(The lines in Pacific Oceans are due to my data... but we get the idea ;) )

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#10
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Charles, I think the one you have on the right might work (don't know what number or filename that image has) - especially of the map I picked as an example - there is not that much fisheries in the Caribbean and off Brazil, so it would be ok if it cuts through there. I can create something similar using the Goode's projection in ArcGIS. I'll keep this in mind when it comes up next time!
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#11
Charles Syrett

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That's the one with a central meridian of 90 east. Geocart doesn't specify the interrupts, but they appear to be 0, 30, 150, and 180.

Charles Syrett
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Charles, I think the one you have on the right might work (don't know what number or filename that image has) - especially of the map I picked as an example - there is not that much fisheries in the Caribbean and off Brazil, so it would be ok if it cuts through there. I can create something similar using the Goode's projection in ArcGIS. I'll keep this in mind when it comes up next time!






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