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Thread: Huge River Paradox

  1. #1
      Ceru is offline
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    Help Huge River Paradox

    Hi, I'm currently making my map for a fantasy series following this tutorial. However, after observing it a little more, I realized there is river paradox going on here. As you can see in the attachment, the dark black lines are where the rivers are supposed to be while the white lines will be the real rivers in the final mapping stage. The biggest white line going down nearly in the middle is where half of the problem is.

    Several dark lines flow from both sides of the mountain and instead of coming together to form a valley or something, they flow north, creating a huge river up there and ending at the west coast. I know and read that all rivers flow downhill hill, but for this map in particular, the smaller rivers are flowing north instead of south, which makes no sense (since gravity pulls everything down, I'm assuming most rivers would flow south because 'south' is 'down') so, I just can't imagain it going up north.

    I am considering whether or not I should just disregard the render (thus why I have a huge white line there, more of which I will add later so that it will hit the sea). However, I then realized why the render came out that way: because down south, there were also mountains so then it kind of made sense why the rivers would be flowing north instead of south... water has to flow somewhere and since there are mountains west, south and east, the only exit left is north... but, how realistic is this? Is it possible for rivers to flow north if there are hills on all sides? Is there anyone out there who knows a fair amount about rivers who can give their thoughts on this?
    Attached Thumbnails Attached Thumbnails Huge River Paradox-river-issues.jpg  

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      Naeddyr is offline
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    Quote Originally Posted by Ceru View Post
    Several dark lines flow from both sides of the mountain and instead of coming together to form a valley or something, they flow north, creating a huge river up there and ending at the west coast. I know and read that all rivers flow downhill hill, but for this map in particular, the smaller rivers are flowing north instead of south, which makes no sense (since gravity pulls everything down, I'm assuming most rivers would flow south because 'south' is 'down') so, I just can't imagain it going up north.

    The pull of gravity on a planet is the sum of all its particles causing a pull on another object, including those in the northern hemisphere. The direction of the pull of gravity is towards the center of the planet. All the stuff on the planet is concentrated around an abstract point towards which they are all pulled, and because a planet is round, that point is at the center of the globe. North and south are defined by the rotation of the planet, not its gravity. Or the orbit of the planet around its star or the rotation of its star etc. north and south are arbitrary.

    Basically, to gravity, it does not matter where on the globe you are, rivers always flow downhill, towards the center of the Earth.

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      isomage is offline
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    Here's a map of the Earth I made using GIMP. It's still a bit rough, but I think it includes all the major features.
    Attached Thumbnails Attached Thumbnails Huge River Paradox-map.png  
    Last edited by isomage; 04-25-2009 at 06:08 AM.
    My random map generators and GIMP scripts: http://axiscity.hexamon.net/users/isomage/

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    Guild Journeyer altasilvapuer's Avatar
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    Quote Originally Posted by Wikipedia
    The Nile [...] is a major north-flowing river in Africa, generally regarded as the longest river in the world.
    - Wikipedia article on The Nile. Some major rivers actually flow from south to north; it's not that uncommon.

    and isomage, I love that 'map'!!

    -asp

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      Ceru is offline
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    Quote Originally Posted by Naeddyr View Post
    The pull of gravity on a planet is the sum of all its particles causing a pull on another object, including those in the northern hemisphere. The direction of the pull of gravity is towards the center of the planet. All the stuff on the planet is concentrated around an abstract point towards which they are all pulled, and because a planet is round, that point is at the center of the globe. North and south are defined by the rotation of the planet, not its gravity. Or the orbit of the planet around its star or the rotation of its star etc. north and south are arbitrary.

    Basically, to gravity, it does not matter where on the globe you are, rivers always flow downhill, towards the center of the Earth.
    Okay, thanks, got it. That makes everything easier to comprehend, but with the way the waters are flowing, it's not flowing to the center of the world. It's going north and then west. Is that possible?

    And thank you altasilvapuer and Isomage for the 'duh' moment. But, I could've sworn the Nile was the only river in the world that flowed from south to north (it was either from a fact sheet or from a teacher -those or I'm wrong again).
    Last edited by Ceru; 04-25-2009 at 08:32 AM.

  6. #6
    Guild Master Gracious Donor Midgardsormr's Avatar
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    Completely forget about rivers and compass directions. The two things are not related. Instead, think about rivers and mountains. Rivers always flow away from the mountain peaks. If they run from one range of mountains toward another, they'll curve away from the second range, much like the rivers in the Midwest United States do. They form downhill from the Rocky Mountains and flow eastward until the land starts to rise headed for the Appalachians, then they curl south toward the Caribbean Sea.

    Rivers that start in the northern part of the Black Hills, though, such as North Dakota's Red River, will flow northward into Canada, eventually reaching the Hudson Bay.

    On Earth, rivers that flow northward are relatively rare, but they do exist. Most are relatively short, but aside from the 4000 mile long Nile, there are three in Russia over 2000 miles (the Lena, Ob, and Yenissey).

    Possibly the most well known river other than the Nile that flows to the north is the Niagara River, though it is only 40 miles long.
    Bryan Ray, visual effects artist
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      Ceru is offline
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    Thanks, I'll keep that in mind when I edit my map again.

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      Naeddyr is offline
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    Quote Originally Posted by Ceru View Post
    Okay, thanks, got it. That makes everything easier to comprehend, but with the way the waters are flowing, it's not flowing to the center of the world. It's going north and then west. Is that possible?

    I just want to make sure: you do realise that when I refer to the center of the planet, I mean the point underground half between Cartoon America and Cartoon China, right? Not a place on the surface, but a point at the middle of the globe.

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      waldronate is offline
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    The reason that you did not get the expected river flow is that there is an outlet to the sea that is lower than the ridge between the bottom and top areas of the map. The attached file shows the the too-high area in red and the too-low area in yellow. If you lower the ridge area and/or raise the low area then your river will flow as desired.

    Another thing you can try is to paint in the desired river channel in Wilbur using a small brush at a fairly low level. Wilbur uses an algorithm that always follows the path of steepest descent and so will always generate plausible river channels by following the terrain. If you give it a desired channel that's lower than the surrounding terrain and connects to your sink (the lowest points or edges of your map) then the river network will follow that path.
    Attached Thumbnails Attached Thumbnails Huge River Paradox-river%2520issues.jpg  

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      waldronate is offline
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    A point of confusion that might need clearing: north, south, east and west correspond to top, bottom, right and left on the images. Up on the map corresponds to out of the screen (lighter pixel values) while down corresponds to into the screen (darker pixel values). I mention this only because it's a fairly common difficulty that people have had when I've explained it before.

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