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I've heard that due to a bug in the terrain generation locations in the positive direction (i.e. (3,5),(100,200)) give more materials such as iron. I can't find any proof this claim, however. Is this true?

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I've seen picture proof of this. Now If only I could find it. –  Raven Dreamer May 6 '11 at 18:01
    
apparently so - it's something to do with the way spawning coordinates for the ores are rounded up instead of down I believe, but I can't remember for sure and can't find the post! –  Alex May 6 '11 at 18:06
    
@Alex - found it. It was (oddly enough) in a minecraft question about iron. –  Raven Dreamer May 6 '11 at 18:07
    
I've just started. As a beginner it's easier to go down first. That's where you set your home. A tiny piece of rock. From there on, I went to -20 and dug at nearly every level. The amount of ore is ridiculous considering the amount of digging. –  ndefontenay May 7 '11 at 3:02
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This was fixed in Beta 1.6. –  Keaanu May 24 '11 at 1:59
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5 Answers

up vote 34 down vote accepted

As of 1.6, this has been fixed.

  • Fixed ore density varying per quadrant from the center of the world

Begin Original Answer

Okay, the original link comes from this answer here.

This, in turn, links to this reddit article, from which the following image is drawn.enter image description here

In addition, one of the reddit comments explains why this appears to be the case, quote:

The bug occurs because of how all ore (and dirt and gravel) are spawned in the game. The game rounds everything towards to 0 (instead of just down), and then adds +0.5 when determining if a block has ore or not. It works for positive numbers (which is the southwest), and doesn't work as well for negative numbers (which is everything in the northeast). They just need to fix the rounding they do.

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Wow, I'm really surprised this isn't better publicized. i.e. every beginning minecraft tutorial should say "DON'T MINE N AND E OF SPAWN" –  authenticgeek May 6 '11 at 18:30
    
Is this still the same for newer maps? I'd heard something about it being fixed. –  The Communist Duck May 6 '11 at 18:40
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@TheCommunist - It might be fixed in 1.6 which is not yet been released. –  Raven Dreamer May 6 '11 at 19:01
    
@Raven Dreamer I just tried it on my (1.5) world, and found this exploit does not occur. Unless, of course, my world is weird. –  The Communist Duck May 6 '11 at 19:03
    
I just redid my test with iron and diamond, and found that they are the only ones affected..and there is a slight difference in concentration. –  The Communist Duck May 6 '11 at 19:06
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This thread discusses the details of this bug, and there is a fix starting from this post - quote below. This was implemented in v1.6:

* Fixed ore density varying per quadrant from the center of the world


I've been looking more closely at the code. I think the culprit actually lies in one of two blocks a short ways below:

int j = (int)(d7 - d11 / 2.0D);
int k = (int)(d8 - d12 / 2.0D);
int m = (int)(d9 - d11 / 2.0D);

int n = (int)(d7 + d11 / 2.0D);
int i1 = (int)(d8 + d12 / 2.0D);
int i2 = (int)(d9 + d11 / 2.0D);

Which amount to truncated start and end indexes for x, y, and z. The source coordinates to the function are absolute block coordinates, so if we're in the SW we're dealing with positive X and Z, and when we're in the NE, we're dealing with negative X and Z.

Or

double d13 = (i3 + 0.5D - d7) / (d11 / 2.0D);
if (d13 * d13 < 1.0D) {
...
double d14 = (i4 + 0.5D - d8) / (d12 / 2.0D);
if (d13 * d13 + d14 * d14 < 1.0D) {
...
double d15 = (i5 + 0.5D - d9) / (d11 / 2.0D);
if ((d13 * d13 + d14 * d14 + d15 * d15 < 1.0D)

Which is computing and testing threshold values for a given block. The computation takes the block coordinate/index, adds a positive offset of 0.5, and subtracts a floating-point position. The 0.5 offset may be the culprit, working as intended for positive position values, but off for negative. I'm even more inclined to believe this when you consider that in the above block we're flooring positive values but ceiling negative ones, which creates a kind of off-by-one condition that could be at play here.

The original thread that investigates the distribution of ores is found here, and contains various images of the distribution.

Quote from the same post:

You can clearly see the different densities, although it's obvious that the number of deposits is about the same. (They should be almost exactly the same.) You can also see the lack of clumping that indicates a non-random distribution.

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It's not obvious to me "the number of deposits is about the same". –  Lohoris May 7 '11 at 8:34
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@Lo'oris Same number of deposits (the spacing in the graphic is the same), but each deposit is larger. –  SevenSidedDie May 7 '11 at 15:49
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Pre-1.6, a rounding bug resulted in the South-West quadrant yielding more ore. The bug is fixed as of 1.6:

  • Fixed ore density varying per quadrant from the center of the world
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Once the world is generated, the ore is "set in stone" so to speak. It won't change the already created blocks so if you have a pre1.6 world you'll still have all the larger deposits in your -,- areas. New areas will be unaffected by the bug if they are generated in 1.6. Just as it's common for long time servers to have areas without new trees or lapiz in the ground.

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I'm usng minecraft 1.5.1 and so far I noticed whenever I go towards the negative direction I find myself in an ocean biome with hardly any islands at all. I found less ore but actually had a cluster of 6 diamonds(or more as I used tnt to mine that cave). On another map I was testing a theory if you player level affected ore spawn and I got around level 52 and went to an extreme hills biome and found 28 emerald ores and about 4 stacks of iron or more and I hadn't even seen lava yet. I also got about 13 diamonds later in that cave so if someone can further test this theory it would help a lot. Note you need to get a high level THEN move to a new unloaded area. I'm sure extreme hills are always generous with ores so that could also be it.

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This doesn't answer the question, and I have a feeling that this is a coincidence. As the other answers have indicated, in previous versions (pre beta 1.6), there was actual code that made ores spawn more in the positive quadrant (for some reason). This has since been fixed. –  Unionhawk Apr 21 '13 at 3:21
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