# Techniques for visualising $n$-dimensional space

Can you guys point me to the types of things I should read about (I'm a maths lay person really) if I want to learn about the current thinking how $n$ dimensional spaces can be visualised and thus navigated?

Sorry this question seems a bit vague, but I'm trying think of how I navigate through data in many dimensions and I feel that mathematicians would have solved these problems many many years ago.

Edit: Thank you for the informed debate: Let me clarify what I'm after. I'm looking at model for navigating data using a computer screen (so 2 dimensions). Add a third dimension (think zoom in zoom out). Ok so what about $n$ dimensions, what techniques could help me navigate them while confining my self o the 3d world of the computer model. Reading the link below to mathsoverflow was interesting and I now have some interesting ideas coming out.

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When you say "maths would have solved these problems many many years ago" what do you mean? What's the problem exactly? I think there's a meta-problem, in that you haven't specified a problem. For example, how do you visualize in $\mathbb R^3$? – Ryan Budney Dec 2 '11 at 3:18

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The old joke is, you first visualize an infinite-dimensional space, then cut down to $n$ dimensions. – Gerry Myerson Dec 2 '11 at 3:19
I'm assuming you mean an n-manifold. Mathematician have various techniques that make it easy to handle larger dimensions. It doesn't mean you can visualize it. 2-manifolds are impossible to visualize i.e. projective space $RP_1$ – simplicity Dec 2 '11 at 3:23
Is this a dupe of this or this? – J. M. Dec 2 '11 at 3:53
– Tony Dec 2 '11 at 3:57
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## 7 Answers

When somebody says "high-dimensional space is hard to visualize", they are thinking of visualizing with the eyes. But mathematicians visualize with the brain!

I highly recommend the AMS article The World of Blind Mathematicians. Who could be better at visualizing things they can't see?

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Thank you I will look into this. – Preet Sangha Dec 2 '11 at 8:49

I'm looking at model for navigating data using a computer screen (so 2 dimensions). Add a third dimension (think zoom in zoom out). Ok so what about n dimensions, what techniques could help me navigate them while confining my self o the 3d world of the computer model.

There is a very large body of published work (both theoretical and applied) on multidimensional data visualization (also called multivariate or $n$-dimensional). Try a web search with these terms! Some example titles:

• Visualization of Multi-variate Scientific Data (Bürger & Hauser)
• A Taxonomy of Glyph Placement Strategies for Multidimensional Data Visualization (Ward)
• Handbook of Data Visualization (Chen, Härdle & Unwin)

and so on. Ward's paper (p. 10) offers some advice when viewing N-dimensional data with a 2-dimensional display, re selecting from the N(N − 1)/2 possible orthogonal views in the N-dimensional space (not including rotational variations).

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I know there is. However as a maths layperson a lot of these are ou t of my depth. Thank you though - I'll follow these up. – Preet Sangha Dec 2 '11 at 21:23

I'm not so experienced with problems in N dimensions but i can suggest one thing: do not confuse the geometry with an analitical process. Also do not confuse when you are talking about mathematical analysis visualizing it with the help of the geometry and viceversa.

The geometry is a really old branch of the math, sometimes someone describe it as a science apart, the thing is that this discipline was born when the human knowledge had to dial with nature very closely and directly, like was during the ancient egipt or in greece. The geometry was born from the observation of the reality, nothing more and nothing less, and the way to express geometry consist in the use of the mathematical language because it is universal and unambiguous.

The analitic process is born to approach and to try to solve other kinds of problems and has to dial with concepts that are not properly available in nature like the concepts of approximation, N dimensions, the laws that we think are the correct ones to describe the natures, the concept of infinite, the infinitely small and the infinitely big, and so on.

The analitic process is really focused on the human needs and only this, if you should describe the lenght of a piece of wood to make a bridge with your hands, you probably do not need to have a really precise measurement, you probably do not need it at all, but if you have to abstract that bridge into a project you probably have to deal with an approximation of that measure, so you need a value, simply because you have to put a quantity on a piece of paper, and thanks to this you can skip from geometry to an analitical process .

You simply can't imagine more than 3 dimension because N>3 does not belong to the world you are in, geometrically speaking.

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N>3 string theorist would debate that. Personally I think you can simulate a being that lives in 4 dimensions on a computer, assuming AI progresses enough to that stage. Then, that being would be able to see in 4 dimensions. With time I think humans could see in higher dimensions. It would be pointless through. – simplicity Dec 2 '11 at 4:08
you say it right "theorist", Preet Sangha is looking for a pratical solution not theories. The human knowledge has switched from geometry to analitical analysis much time ago, the analisys is good when we have to dial with complex problems but is pratically impossible to visualize over N>3, this is the price to pay for us. Also do not confuse the terms, usually the physicist use the verb "describe" and not "visualize" when they talk about N dimensions. – Micro Dec 2 '11 at 4:16

Your best thinking in $\mathbb{R}^2$ and 3 (never $\mathbb{R}$) for counterexamples, but that is it really. I mean everything's 'the same', especially if you consider (I know this is lin. algebra but the point is emphasized more strongly with open balls) open balls in $\mathbb{R}^n$. Literally everything you need to 'know' from an open ball will be 'seen' from a picture of a disc or sphere [i.e $\mathbb{R}^2$ = union of open balls centre zero and radius n; similar results for $\mathbb{R}^n$]. You can also 'move' open balls as $B(r,a) = a + rB(1,0)$. I don't want to go into too much detail and these examples are terrible but basically $\mathbb{R}^2$ and $\mathbb{R}^3$ will usually be fine for counterexamples, there is an obvious decomposition (though not 'best') of $\mathbb R^n$ into direct sums of the subspaces $\mathbb{R}^2$ and $\mathbb{R}^3$ (and $\mathbb{R}$), etc.

It is obviously best not to work in $\mathbb{R}^n$ often though, $(\mathbb{Z}_p)^n$; vectors with entries modulo $p$ for prime $p$ is an important example. There are two other obvious important vector spaces, but both of these are easy to visualize for counterexamples.

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I know this was a poor answer (due to the poor 'problem' posted - a meta problem), but downvotes with critism are more useful than downvotes for everyone. – Adam Dec 2 '11 at 3:29
This is very confusing. Firstly, open balls in $R^4$ are wildly different than open balls in $R^3$. Even, then there are objects in $R^4$ that are impossible in $R^3$ like Klein bottle. – simplicity Dec 2 '11 at 3:30
?? It is trivial to come up with specific examples to emphasize how things are different but they are not wildly different (whatever that means). Consider proving that a compact set is bounded in R^n. Well note from the example of R^2, R^n is the union of open balls centered at 0 with integer radius so it is clear we can find a big enough ball to contain the set hence bounded. Say we want to prove the union of subspaces is not a vector space - take two different lines in R^2, easily extended (by embedding R^2 into R^n) ... I could go on, I think you are missing the point however. – Adam Dec 2 '11 at 3:35
However, I think you missed what OP wanted. Also, that doesn't work all the time so it's misleading. There is probably crazy objects in $R^4$ that don't look like anything in $R^3$. Well, I can give several if you like. – simplicity Dec 2 '11 at 3:52

Check out http://en.wikipedia.org/wiki/Parallel_coordinates if your data is discrete, it maybe very useful. If it is not, there are extensions but they are not always insightful.

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I sometimes like to pervert the standard "perspective" 2-D rendering of the $x,y$ & $z$ axes in $\mathbb{R}^3$ by drawing $n$ axes through a common origin all with highly acute angles between them, which I imagine are all pairwise perpendicular (for each of the $\binom{n}{2}=\frac{n(n-1)}{2}$ pairs of axes) and sometimes even indicate this with the little right angle indicators (parallel to each alternate axis in a pair) -- as if I am looking from some yet other unspecified, distant dimension. But it requires of course some imagination, and complements rather than replaces other, non-visual ways of conceptualizing $\mathbb{R}^n$.

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I would like to say that you can't visualize higher dimension in Mathematics. Even for n=4 it is impossible. Several barriers that stop you from doing it. If you take the 2-manifolds you have really three objects i.e. the sphere, the torus and finally projective space. The problem is even for closed surfaces you would think that it's easy to visualize, however the projective space can't be realized properly in $R^3$ i.e. can't be embedded into it(this mean it crosses itself like the Klein Bottle does). You would need to go into the fourth dimension.

This is a popular image of the Klein bottle. But, in reality this shouldn't intersect itself. However, it's impossible to visualize it because you would need to think in 4 dimensions. Mathematics has got around this problems by developing topology and algebraic methods.

The naive way to visualize the Klein Bottle is to find the points in which it intersects itself in $R^3$ and then give them another colour and say they are in the 4th dimension.

3-manifolds are even more impossible to visualize. 3-spheres would look crazy

There is no true way to visualize it. Everything is really just algebra mainly group theory mixed with topology.

If you really care to learn all this it's best to pick up any decent book on Topology and read it. Armstrong Basic Topology is the best place to start. Would like to add that the 4th dimension is the hardest dimension possible you can get. http://en.wikipedia.org/wiki/Exotic_R4

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thank you. I will look up topology – Preet Sangha Dec 2 '11 at 8:36
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