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Thread: Is this a viable world river system?

  1. #1

    Question Is this a viable world river system?

    I have tried to create a realistic river system for the world I am working on based on the information I got from the Sticky post "How to get you rivers in the right place" by Ryan K. I think I have done that, but I wondered if some more experienced map makers might take a look at my work. The map is 6,000 miles by 6,000 miles and is representative, at this point. The rivers shown are major river systems. I have included the 30th parallel in order to show the dry/arid zones and the wet zones to the north.

    The area marked "A" is an experiment. I don't know if it can function this way. The south side of the mountain chain is in a rain shadow. The rivers flowing out of it are from the substantial snow melt cascading out of the valleys south. There are a few elevated mountain lakes, and the system then flows in to an expansive and very dry savannah. I intended for the map to show a varying flow river system collecting in a dry lake bed, filling, and evaporating seasonally (much like the African savannah without the torrential storms). I am wondering if that situation is realistic, and, if so, is it clear on as presented on the map?

    Thanks for any help.

    Click image for larger version. 

Name:	Abathas WIP River System.jpg 
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  2. #2
    Guild Expert Gracious Donor Hai-Etlik's Avatar
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    That river looks fine. There are plenty of 'endorheic' lakes like the Caspian Sea, Great Salt Lake, etc, and there are also rivers that simply spread out into an inland flood plain and evaporate like the Okavango.

    The long river in the northeast though seems to be following along a raised area of hills (though it's hard to interpret without contours) Those huge lakes up in the mountains without much of a catchment area feel a bit off too.

    Overall, you've got the basic idea.

    As a bonus bit of criticism, you've got a problem with your projection. You seem to be using a Equidistant Cylindrical projection (Parallels are all evenly spaced and vertical distances are all to scale.) However, that would produce severe distortion at the higher latitudes.

    Take a look at the map of Earth here: http://en.wikipedia.org/wiki/Equirectangular_projection

    See how the parallels (Horizontal grid lines) are evenly spaced, but horizontal distance gets stretched out more and more as you move away from the equator.

    Along the N 60° parallel near the top of your map, distances are only half what they are at the equator (So the map is only 3000 miles wide at 60°). And at the very top, which appears to be about N 75°, it's just a little over one quarter the width at the equator, 1553 miles wide. Even at just N 30° the map is 5196 miles wide. There's no way to have a square 6000 miles on a side on the surface of a sphere 3820 miles in radius.

    Unfortunately there's no easy solution or rule of thumb. All projections cause distortion. If you are most concerned with shape, don't care much about distance, and aren't worried about the poles, Mercator is your best bet. It stretches in BOTH directions as you move away from the equator which means things tend to stay the same shape.

    My recommendation would be to move the N 60° line upward and call it a Mercator map. You'd be able to retain '6000 miles' along the equator, but away from the equator the scale would change.

    You can get a graticule (Grid) for a Mercator map here: http://www.cartographersguild.com/sh...ector-Template

  3. #3

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    Quote Originally Posted by Hai-Etlik View Post
    That river looks fine. There are plenty of 'endorheic' lakes like the Caspian Sea, Great Salt Lake, etc, and there are also rivers that simply spread out into an inland flood plain and evaporate like the Okavango.

    The long river in the northeast though seems to be following along a raised area of hills (though it's hard to interpret without contours) Those huge lakes up in the mountains without much of a catchment area feel a bit off too.

    Overall, you've got the basic idea.
    If the river you are referring to is to the right of the forest,then it's flowing between the raised hills and the raised elevation from the mountains to the east. I am not fond of that river. It was one of the first ones I attempted, and I had already considered removing it altogether or redesigning it.

    Are you referring to the lakes in the hills north of site "A"?

  4. #4

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    Quote Originally Posted by Hai-Etlik View Post
    As a bonus bit of criticism, you've got a problem with your projection. You seem to be using a Equidistant Cylindrical projection (Parallels are all evenly spaced and vertical distances are all to scale.) However, that would produce severe distortion at the higher latitudes.

    Take a look at the map of Earth here: http://en.wikipedia.org/wiki/Equirectangular_projection

    See how the parallels (Horizontal grid lines) are evenly spaced, but horizontal distance gets stretched out more and more as you move away from the equator.

    Along the N 60° parallel near the top of your map, distances are only half what they are at the equator (So the map is only 3000 miles wide at 60°). And at the very top, which appears to be about N 75°, it's just a little over one quarter the width at the equator, 1553 miles wide. Even at just N 30° the map is 5196 miles wide. There's no way to have a square 6000 miles on a side on the surface of a sphere 3820 miles in radius.

    Unfortunately there's no easy solution or rule of thumb. All projections cause distortion. If you are most concerned with shape, don't care much about distance, and aren't worried about the poles, Mercator is your best bet. It stretches in BOTH directions as you move away from the equator which means things tend to stay the same shape.

    My recommendation would be to move the N 60° line upward and call it a Mercator map. You'd be able to retain '6000 miles' along the equator, but away from the equator the scale would change.

    You can get a graticule (Grid) for a Mercator map here: http://www.cartographersguild.com/sh...ector-Template
    That had not even occurred to me. This is my first map that wasn't drawn on graph paper. I have downloaded your svg file for use with GIMP. I have two days off so I will try to post something soon. Thanks for all of the help.

    EDIT:
    I have added my Mercator work thus far. Am I doing this right? I had to move it south in order for the equator to match my earlier works. The relative latitudes are going to change a lot about the world I thought I was building.

    Click image for larger version. 

Name:	Abathas Mercator Test.jpg 
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    Last edited by Porklet; 06-13-2011 at 11:10 PM.

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    Guild Expert Gracious Donor Hai-Etlik's Avatar
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    Quote Originally Posted by Porklet View Post
    EDIT:
    I have added my Mercator work thus far. Am I doing this right? I had to move it south in order for the equator to match my earlier works. The relative latitudes are going to change a lot about the world I thought I was building.
    I'd say you've got it quite a bit too small.

    I would suggest you try to line up the equator with where you had the equator before, and the N 30° meridian (The second one up from the equator) with where you had it before. All the others will be different, but as those were apparently the ones you were focusing on, it makes sense to keep them same.

    To simplify it, I've chopped out the part of the graticule you need to do that:

    Click image for larger version. 

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  6. #6
    Software Dev/Rep Gracious Donor waldronate's Avatar
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    Imm not sure that a Mercator projection would be a particularly good choice because of the rather extreme distortion heading northward. A simpler cylindrical projection might work, as might something like a Mollweide projection. I pulled out my elderly and creaky ReprojectImage program ( http://www.ridgenet.net/~jslayton/ReprojectImage.zip - although something like Hugin or any number of other image reprojection programs would also work here) and used a Mollweide projection on the basic image. Pulling back onto a sphere gives the last screenshot. If you have a flat map that you're starting from and aren't terribly worried about some distortion, then I really recommend picking a projection that will keep the latitudes at a slight expense of longitudes (unless it's absolutely critical that some points be exactly north or south of others).

    As far as the river that you were asking about, two real-world examples are the Okavango delta in Africa ( http://en.wikipedia.org/wiki/Okavango_Delta ) and what was Tulare Lake in California's central valley ( http://en.wikipedia.org/wiki/Tulare_Lake ). Both had annual floods that spread out over many, many square miles and revert to grassland and/or marshes after that passes. Neither one has a whole lot of rainfall in the actual areas that flood, but collect rain from elsewhere.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	Abathas ReprojectImage.jpg 
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ID:	36512   Click image for larger version. 

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Name:	Abathas ReprojectImage Reprojected.jpg 
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ID:	36514  
    Last edited by waldronate; 06-14-2011 at 01:06 AM.

  7. #7
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    Quote Originally Posted by waldronate View Post
    Imm not sure that a Mercator projection would be a particularly good choice because of the rather extreme distortion heading northward. A simpler cylindrical projection might work, as might something like a Mollweide projection.
    Yes, Normal Mercator really isn't the best option for a continent map, but I suggested it as it's far and away the simplest option that can be implemented without needing additional software. If I were trying to map a continent this size and shape for general reference, I'd probably use a Chamberlain Trimetric projection but that's well beyond what I want to throw at a newbie.

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    Software Dev/Rep Gracious Donor waldronate's Avatar
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    I'm a firm believer in additional software!

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    Guild Expert Gracious Donor Hai-Etlik's Avatar
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    Quote Originally Posted by waldronate View Post
    I'm a firm believer in additional software!
    In the long run, I certainly agree: my most recent map used about 7 different programs, two which I wrote myself. But I didn't want to overwhelm Porklet by introducing too much at once.

  10. #10

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    Quote Originally Posted by waldronate View Post
    Imm not sure that a Mercator projection would be a particularly good choice because of the rather extreme distortion heading northward. A simpler cylindrical projection might work, as might something like a Mollweide projection. I pulled out my elderly and creaky ReprojectImage program ( http://www.ridgenet.net/~jslayton/ReprojectImage.zip - although something like Hugin or any number of other image reprojection programs would also work here) and used a Mollweide projection on the basic image. Pulling back onto a sphere gives the last screenshot. If you have a flat map that you're starting from and aren't terribly worried about some distortion, then I really recommend picking a projection that will keep the latitudes at a slight expense of longitudes (unless it's absolutely critical that some points be exactly north or south of others).
    I am frightened. I had no idea the chain of islands in the NW was on the other side of the planet.

    I have downloaded the Reproject software. I am toying with it now. I have a sense of how to use the X/Y/Scale stats on the left using your original picture as a guide. I am using this software to accurately show where land masses lie on a sphere of a particular size, no? This may sound ignorant, but I am still a little confused. Thanks for your help.

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