## No One Knows How Long the US Coastline Is (discovermagazine.com) 189

How long is the U.S. coastline? It's a straightforward question, and one that's important for scientists and government agencies alike. From a report:

*The U.S. Geological Survey could give you an answer, too, but I'm going to tell you right now that it's wrong. In fact, no one could give you the right answer, and if you look around, you'll find a number of estimations that differ by seemingly improbable amounts. One government report lists the number as 12,383 miles. The same report admits that a different government agency says the figure is actually 88,612 miles. That's an almost eight-fold disparity for a fact that seems simple to obtain. We all know how to use a ruler, right?*

Well, we all know how to measure a straight line, but what about a curve? And what if that curve has curves? The crux of the problem comes down to geometry, and the fundamentally uneven nature of coastlines. Though the border between land and sea may look fairly straight when seen from far away, they're anything but. Coastlines jut and dip, curve and cut, and each deviation from a straight line adds distance. Some of these features are massive, like bays, while others are miniscule.Well, we all know how to measure a straight line, but what about a curve? And what if that curve has curves? The crux of the problem comes down to geometry, and the fundamentally uneven nature of coastlines. Though the border between land and sea may look fairly straight when seen from far away, they're anything but. Coastlines jut and dip, curve and cut, and each deviation from a straight line adds distance. Some of these features are massive, like bays, while others are miniscule.

## +/- 12,383 miles (Score:1)

## Re: (Score:3)

https://en.wikipedia.org/wiki/... [wikipedia.org]

The best answer I can give is >0.

## Re: (Score:2)

If I had to pick any one value I would have given exactly zero.

If water is described as "water molecules with gaps between them" Then water is essentially everywhere in the USA and there is no natural closed boundary that excludes it, the whole of the USA is an underwater rock formation.

## Re: (Score:2)

## Re:+/- 12,383 miles (Score:5, Informative)

Isn't "coastline" the very first example they give in Fractals 101?

It certainly was back in the 1980s when I was at school but here it is as front page news on Slashdot. FFS.

Now get off my lawn.

## Re:+/- 12,383 miles (Score:4, Funny)

No, coastlines are the second example. Snowflakes are the first.

## Re: (Score:2)

And yet, how correct you are... just depends what snowflake you're talking about.

https://youtu.be/HvXbQb57lsE?t... [youtu.be]

PBS Nova - Fractals - Hunting the Hidden Dimension

## Re: (Score:3)

Australia defined a standard about how big a feature had to be to be regarded as "coastline" - same with rivers mouths and the like. Once this was defined, then anything outside of this definition no longer counted, and the coastline was measured quite accurately, in a way that if measured in the future, could identify whether the coastline was shrinking or expanding.

eg: https://ebrary.net/10179/manag... [ebrary.net]

## It's infinite. (Score:5, Insightful)

Coastlines are fractal and have 1.4 dimensions. This does mean Cthulhu could break out at any moment.

## Re:It's infinite. (Score:5, Insightful)

Coastlines are fractal and have 1.4 dimensions.

And being fractal makes the initial question of "how long" meaningless. To what resolution? If you look at the molecular level, it is nearly infinite. If you look at the sand grain level, less so. If you look at one foot intervals, even less so.

That of course leaves the question of how you define the coastline. It's not just bays and similar features that create issues, but AT WHAT TIDE LEVEL? Do you define the "coast" as being at the mean high high water (MHHW), mean sea level (MSL), high water line, or where? Do you count both sides of the Outer Banks in North Carolina, both sides and the inner edge of the sounds behind them, or just the outer edge?

The question is also meaningless because it changes nothing. Nothing changes if you say that the US coast is 1,000,000km or 200,000km or 1km. If you're estimating how much it will cost to install coastal protection you will measure how long the protection measure is, not how long the coast is behind it.

So, must be a slow news day at /.

## Re: (Score:2, Informative)

It is certainly wrong to say it is 1km. There is a lower bound to the length of a coast line. It can not be shorter than the longest straight line distance between any two points on the coast line.

## Re:It's infinite. (Score:4, Interesting)

It can not be shorter than the longest straight line distance between any two points on the coast line.

Of course it can.

A: Not all land between points of coastline is coastline. We don't even have a solid definition of coastline to start measuring.

B: In strict 3 space, measuring coastline makes little sense. Lines are 2D, the coast is 3D, and you first need strict rules for tracing the path before you can measure it. How do you handle a cliff on a beach? What if it juts out over the water? When considering 2D projections, it makes a bit more sense. But "the longest straight line distance between any two points on the coast line" in such a projection is infinite. Consider "the longest straight line distance between" your dick and your ass based on a 2D projection (flat map) of Earth. That line would simply wrap around the Earth forever in an infinitely tight spiral. Or consider the simpler scenario of wrapping around Earth once. That's "the longest straight line distance", yet we can show the actual distance is shorter, even if we don't know the true position of either point. Start by drawing a bounding box around each point with whatever accuracy/precision we want / can achieve, then measuring the distance between the outer edges of the bounding boxes. This gives us an upper bound for the actual distance. (You can simply draw a line segment between the points, then draw lines perpendicular to that segment at each point, and find where those lines intersect the bounding boxes to determine the "outer edge" of each bounding box.)

## Re: (Score:3)

It can not be shorter than the longest straight line distance between any two points on the coast line.

Of course it can.

A: Not all land between points of coastline is coastline. We don't even have a solid definition of coastline to start measuring.

Instead of a straight line through three-dimensional space, the shortest possible length would be the length of the shortest line between two points (for the surface of a sphere, I think it's part of a Great Circle). Any way that the coastline deviates from that line must increase the length, since by definition that line is the shortest possible line connecting those two points. You also have to add the requirement (which the GP probably just left unstated) that you measure each contiguous coast separately

## Re: (Score:2)

Congratulations, you win a gold medal in pedantically overcomplicating things and completely missing the point.

If I say "longest straight line I can draw on the US West Coast", it's pretty obvious I'm talking about a line from the NW tip of Washington to the SW tip of California, in a direct "as the crow flies" path, not spiralling around the fucking planet. The word "LONGEST" in this CONTEXT means "the farthest two points from each other you can find" on the coastline.

## Re: (Score:3)

And where is the NW tip of Washington State? Point Roberts? Then you have to consider the coast enters Canada for a while before rejoining Washington (Point Roberts is only accessible by land from Canada). One of the San Juan Islands? Then you have a length of no coast line.

## Re: (Score:2)

You're missing the forest for the trees.

The point is that we can easily establish a MINIMUM. Nitpicking over what would exactly would constitute maximums is completely missing the point.

## Re: (Score:3)

## Re: (Score:2)

"The West Coast" typically only includes California, Oregon, and Washington. If you want to include Alaska, it would be more accurate to call it "the US Pacific Coast". But then that may logically include Hawaii as well.

## Re: (Score:2)

And to that end, so there's no confusion, I say, "As the worm crawls."

## Re: (Score:2)

You called, sir?

## Easier counterexample (Score:2)

There's a far easier counterexample, that works in 2D even. Imagine a circle that is an island. Choose any two points. The longest, when they are opposite, straight line is a distance - lets call it d or 2r. It's totally less than the coastline, by a ratio of about 7:22.

## Re: (Score:2)

The clown I replied to stated that the coastline could never be shorter than that distance.

You're doing it backwards.

## Re: (Score:2)

Ah, okay, fine, then the island should look like a "U". Either way, easier choices.

## Re: (Score:3)

Don't forget waves or kids playing on the beach.

I'd argue the length of the coastline is exactly what the surveyors office says it is. It is a matter of definition, not measurement. There is no coastline on the beach, only on maps.

While I'm at it, if a tree falls in the forest, there is a sound. The standard definition of sound does not require a human listener. The sound of one hand clapping? I can clap with one hand. It sounds almost like clapping with two hands.

Fractals are cool. Cooler than coastlines.

## Re: (Score:3)

"The sound of one hand clapping? I can clap with one hand."

The action you are likely performing is not generally recognized as 'clapping'. So the sound it makes is irrelevant.

"The standard definition of sound does not require a human listener."

What so-called "standard definition of sound" are you using? I just checked two separate dictionaries and both of them defined sound in terms of sensing vibrations on the auditory structures of an ear as their first definition of sound (noun).

"I'd argue the length of

## Re: (Score:2)

What so-called "standard definition of sound" are you using? I just checked two separate dictionaries and both of them defined sound in terms of sensing vibrations on the auditory structures of an ear as their first definition of sound (noun).

I was referring to the one used in sentences like "I recorded the weird sound my car makes". It is generally assumed you used a microphone to record vibrations in the air and not electrodes in the brain to record the vibrations there. Also technical measures like sound pressure use non-human-brain based definitions of sound.

Clearly there are wrong answers though. 1 mile is clearly wrong. Equally clearly there is no limit to the number of correct answers, but it depends on methodology -- so first you set a methodology, then you make your measurements according to that methodology. The stricter and more well defined the method, the stricter and more restricted the range of values that will satisfy it.

I believe we are in agreement. The only thing I would add is that a fine grained method would probably have to rely on arbitrary judgement calls. For example, if a kid digs a new 5cm wid

## Re: (Score:2)

And being fractal makes the initial question of "how long" meaningless. To what resolution? If you look at the molecular level, it is nearly infinite. If you look at the sand grain level, less so. If you look at one foot intervals, even less so.

Agreed. It's a meaningless question, and any answer will be just as meaningless, if not more so.

## Re: (Score:2)

but AT WHAT TIDE LEVEL?

Next click-bait headline:

Our country expected to lose 20% of its coastline at low tide!

## Re: (Score:2)

## Re: (Score:2)

No real coastline is infinite, because real coastlines are made up of matter which is made up of atoms, not mathematical idealizations. Only mathematically ideal coastlines are infinite. You can, of course, create many different measures for the length of the coastline, some of which will be much much longer than others (but also useless), but all of them will be longer than some number (a strict lower limit would be the size of the "rectangle" that contains the US minus the length of the box that crosses o

## Re: (Score:3)

Ah, but atoms are composed of quantum particles, which strictly speaking have neither a definite size nor position, but rather a wave-function that extends to the farthest reaches of the universe with non-zero probability. The circumference of even a single electron is thus exactly equal to that of the entire universe, which may or may not be infinite.

Unless you impose some completely arbitrary cut off point (e.g. there's a 99.99999999% chance that the atom will resolve as being within this area when its w

## Re: (Score:2)

> quantum particles, which strictly speaking have neither a definite size nor position,

Did you miss the memo that the wave function collapses [wikipedia.org] when you

measurethem?> truly accurate measurements of size will be infinite.

Total nonsense. The Planck Length [wikipedia.org] isn't zero. It is a discrete amount. Furthermore we

aren'tmeasuring at the sub-atomic level. Accuracy +/- of some _#_ meters is more then "good enough". i.e. 33,333 km +/- 10 km.## Re: (Score:2)

But only for the instant of the measurement - as soon as you look away to write your report it'll be infinite again.

What does the plank length have to do with anything? I'm not talking about fractal limits, in which case it would most certainly would put an upper bound on length (though at ~10^25 plank lengths across a hydrogen atom, it's going to be a VERY high bound)

I'm talking about the fact that we know with certainty that every quarticle in a baseball has infinite "size", but you want me to believe th

## Re: (Score:2)

Did you miss the memo that the wave function collapses [wikipedia.org] when you measure them?

Wave function collapse is a feature in some interpretations of quantum mechanics. There are also interpretations that don't require a collapse.

## Where do you draw the line? (Score:3)

We have rivers that fan out into the ocean. How far up the river do we go until we are no longer at the coastline. I want to sell my home to be on the coast even though it is hundreds of miles away from the ocean and thousands of feet above sea level, however there is a little stream next to my home, which leads to a creak, that leads to a river, which leads to a larger river then goes into the ocean.

## Re: (Score:2)

## Re: (Score:2)

Several years living in Willingboro NJ, near the Rancocas creek... I remember that the river there had a visible tide. (It's been 47 years, but...) I remember its amplitude being far less than the effect at the beach. This is about 4 miles up the creek from the Delaware river, about 40 miles from the mouth of the Delaware.

I'm guessing that doesn't count as "coastline"....

Off-topic: The specific place where I saw the effect was at what is now the end of Bridge Street but at the time had a bridge that had at

## Someone just discovered fractals! (Score:5, Informative)

The coastline problem is literally a textbook example of fractals. The "size" of the object (perimeter, area, etc.) depends on the scale at which it is measured (the size of the "ruler" one uses). A coastline has finer and finer features as one zooms in, so the overall length/perimeter one computes is larger and larger as one uses a finer resolution. For a perfect/mathematical fractal, the coastline could actually be infinite in length.

This is absolutely interesting. But also not new. Everyone with a passing familiarity with measuring coastlines knows about this issue.

## Re: Someone just discovered fractals! (Score:5, Funny)

Fifth-grade news for nerds.

## Re: (Score:2)

Fortunately for us, the dimensions of quarks quantize the possible values somewhat, so it is finite, but large. Still, do you go across one side of each atom, or do you go all the way around each one until the closest point to the next?

## Re: (Score:3)

And if you go "around" an atom, and at what state of excitement do you measure it in?

## Re: (Score:2)

## Re: (Score:3)

Except quarks, like all quarticles, don't have a well-defined circumference. Instead they have a quantum wave function that extends to infinity with non-zero probability. To make any non-infinite measurement you must first impose an arbitrary cut-off point on that probability.

## coastline paradox (Score:1)

https://en.wikipedia.org/wiki/Coastline_paradox

## Mandelbrot beat them (Score:5, Informative)

Mandelbrot's* well-known "How Long Is the Coast of Britain?" article (published in 1967) starts with this question - and it goes on to discuss self-similar curves that are a type of fractals.

*: yes, he is the guy who came up with the Mandelbrot fractal

## Re: (Score:2)

Yep. And it's silly to even attempt to find an exact measure for that very reason. The best you can do is set a somewhat arbitrary cut-off, and measure to that standard. Anything else is just a waste of time.

## Re: (Score:2)

This is exactly it; the question of how long the coastline "really" is is of no interest to "science" or government or civics or any physical human activity: all that matters is the establishment of a system that gives predictable values that are "good enough" to keep most people from fighting over them. That's all. Make a rule; measure to the rule. It is useful to know generally how much coastline one place has in comparison to another place, but the details don't matter.

Scientifically it is a nonsense que

## Re: (Score:2)

Mandelbrot's ... yes, he is the guy who came up with the Mandelbrot fractal

Not quite! The Mandelbrot set* as the index set for stable/connected Julia sets was known by Fatou and Julia [wikipedia.org] around 1920. It was later named in honour of Benoit Mandelbrot.

*I sat through a three-lecture series by Mandelbrot in 1999 when I was an undergraduate in Cambridge. I distinctly remember him saying "The Mandelbrot set is not a fractal. It's beyond fractals." In simple terms, I think he referred to the fact that it's the edge of the set that is a fractal; like coastlines, the length of the edge dep

## Re: (Score:2)

It all depends on what you mean by "fractal." The term has no precise mathematical meaning.

## Re: (Score:2)

It all depends on what you mean by "fractal." The term has no precise mathematical meaning.

If you're going to dispute something that Mandelbrot himself said about fractals, then please provide some more info. I have merely studied fractal geometry as a part of my advanced math studies. I would say anything with a non-integer dimension is a fractal. Of course, you'll have a bunch of different definitions for dimension [wikipedia.org], but they generally agree in the sense of defining which objects are fractal. In this case, the edge of the Mandelbrot set has a dimension between 1 and 2.

## Re: (Score:2)

I'm not disputing anything that Mandelbrot said. He himself walked back from a formal definition of a fractal, and ultimately chose not to give a precise mathematical definition. From the second edition of Mandelbrot's book (on page 459):

In the first edition of the book, Mandel

## It seems straightforward, but it's not. (Score:3)

This comes down to the resolution used. Think fractals. What's your minimum measurement unit? 10km? 1km? 100m? 10m? 1m? 10cm? 1cm? 1mm? Smaller?

The smaller the unit of measurement, the larger the coastline, as you can cover smaller and smaller details.

Then it's the question of where to place the coastline. High tide? Low tide? Middle? What about the "type of coastline"? It seems obvious if it's rock .. but what if it's sand? Where do you put the line?

## Coastline Paradox (Score:2)

There's a famous paper by Mandelbrot on the question of coastlines: "How Long Is the Coast of Britain? Statistical Self-Similarity and Fractional Dimension".

In short, coastlines are fractal and effectively have infinite length.

https://en.wikipedia.org/wiki/... [wikipedia.org]

## Re: (Score:2)

It was mentioned in Gleick's book "Chaos" - one of the first mainstream books about the subject. I read it when I was an undergrad and I'm, ummmm, not young (though my apparent age varies depending on what size calendar you use).

## Re: (Score:2)

## Re: (Score:2)

Now

thatis exactly the information that should have been put in the summary.## Minimum measured feature size (Score:2)

Everyone competent knows how to measure the lengths of curves, and curves that have curves. The issue is that based upon your use case and needs, different people pick what are essentially different resolutions for their mapping and length measurements, which means that you discard the lengths of featur

## Needs another standard of measurement (Score:1)

## Re: (Score:2)

I like this answer. The words "practical" and "standard" are underrepresented in these comments, but that's the most practical standard I think I've seen suggested.

When I saw this article pop up, I thought perhaps there would be a discussion about competing standards and how practical each was. I understand the philosophical question that isn't fully resolvable, but I was thinking of ways that you could get consistent answers and was disappointed not to see more posts along that line.

Perhaps you draw a stra

## Re: (Score:2)

Low tide or high tide? What do you do about rivers? Fjords? Streams?

## Complex questions (Score:2)

Islands, salt water, fresh water., rivers, streams...

Do we include Puerto Rico and other US territories?

## Re: (Score:2)

Wait, didn't Debt Island sink? Did it float back up?

How much coastline does Bermuda have during a storm?

The real absurdity of it comes when you consider coastal salt marshes, which is a lot of land. Are brackish swamps land or sea? Do you have to measure how far the water goes up the mangrove trunks at high tide? How many days of the year the dirt is exposed at low tide?

## It varies with the tides (Score:1)

## Measuring contest (Score:1)

Give it up, USA: no matter how many coastline lengthening ads you respond to, yours will never be as long as that of the country next door. Don't worry, coastline size isn't

thatimportant.## Non-Scientific Language Question (Score:5, Insightful)

As usual, the question isn't specific enough to have an answer. Therefore, people think it's difficult to answer.

The answer is very simple, ask for what you want.

Maybe it's how far a ship would need to travel to get to any point -- ships take gentle curves. Maybe it's how long would it take to see it all on-foot -- humans take 1-yard-long straight lines.

Another stupid question: which came first, the chicken or the egg? Again, a language question. Define the word "egg" and it's easy.

If "egg" is any egg, then dinosaurs had eggs long before chickens.

If "egg" is "chicken egg", then define "chicken egg".

If "chicken egg" is an egg laid by a chicken, then the chicken came first, by your own definition.

If "chicken egg" is an egg from which a chicken hatches, then the egg came first, by your own definition.

Stupid questions are questions that only exist because of the manner in which you formed the question itself.

As my associate likes to say: "the answer is 6. there. now, what are you going to do with it?"

Decide what you actually want to know -- that means how you're going to use the information. Ask that question. There won't be anything crazy about it.

How long is a shoreline? Tide in or out? At what depth -- does a puddle ruin everything? Footprints? What about waves lapping on the beach?

Hey, what about the birth from a river?

Do we include the entire river?

Where does the river become the ocean?

Right, that's easy, it's where the fresh water changes to salt water.

How do you want me to measure that, given that the river's "fresh" water has dirt in it.

At what level of salinity does your version of "fresh" water become your version of "salt" water?

Arbitrary trivia is arbitrary from the start. Decide what you're doing. Are you designing battleships, or water-ways for salmon? I promise, the navy doesn't agree with the fish, and they don't need to.

## Re: (Score:2)

It isn't as obvious however that this is arbitrary.

Think of the usual "how long is a piece of string" question. That is arbitrary. However when you say "how long is THIS piece of string" it ceases to be arbitrary. Now a string is flexible and can be stretched out then measured end to end to come up with an exact answer.

By logical extension the costline can as well, except it can't due to the fractal problem. And this is where I'm getting to: With this line of thinking the intuitive answer is that there shou

## Re: (Score:2)

You've missed your own mistake.

Substitute your "string" that you said "is flexible and can be stretched out then measured" with a straight piece of elastic band.

You can say "THIS" elastic band as many times as you'd like. But "THIS elastic band" has multiple configurations. An infinite number of configurations. It stretches, it compresses, it collapses, and it breaks.

So, would you measure my elastic band at full extension? Full compression? Zero tension? The tension for which it was designed to be use

## Re: (Score:2)

I think you just re-enforced what I said with an equal but different example.

Arbitrary involves arbitrary words.

Non-arbitrary involves pointing to something specific: "THIS". Additional knowledge is required to realise that it is in fact arbitrary.

This string can be measured. By extension everything specific we point to should be measurable.

But wait this border can't be measured because there's an additional factor (fractal problem) that affects its length.

But wait this rubber band can't be measured because

## Re: (Score:2)

It was an interesting thought experiment until the discovery of DNA, but now we understand that the egg clearly comes before the chicken.

Where you draw the line between what you call a "chicken" and what you would consider a proto-chicken is arbitrary, but wherever you draw that line, a proto-chicken laid the first egg that would grow into a chicken.

If you go back far enough, when the egg shell was first invented, the proto-bird and proto-mammal were the same. We came out of the shallow sea together, the ma

## Chicken and egg (Score:2)

I don't get the "chicken or the egg" dilemma. I haven't tried "researching" it, but it always seemed obvious to me that the answer is "the egg".

We just have to go back to the first chicken. The definition of the "first chicken" is that while it is a "chicken", its parents are not. Sure, it would be hard to actually define at which point back we stop considering the ancestors chickens, down to the specific mutation, but we do have to stop at some point.

So, you have "not chickens", producing an egg which give

## Easy, just make a new unit! (Score:5, Funny)

The length of the US coastline is equal to... 1 US Coastline. Good luck with conversions to metric, though - we hate that here in the States ;)

## Re: (Score:2)

How many laps around the library of congress building is that?

## Re: (Score:3)

How many laps around the library of congress building is that?

Exactly 1, the Library of Congress is already inside the land border!

## I volunteer to measure it (Score:2)

I will create a KickStarter to fund my measurement of the US coastline. It will obviously require a significant amount of logistical support, so I will conservatively pick $25 million US as “fully funded”. If we don’t hit that target, I will still use the donations to fund a measurement of a section of the coastline for now - probably part of Oregon, or perhaps one of the Hawaiian Islands.

## This is about 40 years old (Score:2)

## almost eight-fold? (Score:2)

Now slightly more than 7 means almost 8?

7.16x is not closer to 8x than 7x.

## Re: (Score:2)

7.16x is closer to 8x than 4x, and what kind of heathen uses non-power-of-two multipliers?

## Terrible Summary (Score:2)

This summary starts by assuming that the information is important, and that the inability to clearly define that piece of information is bad.

The article does not explain why knowing the precise amount of coastline *is* important.

Because it probably isn't that important.

## Re: (Score:2)

It's important for all sorts of different reasons, the "problem" (for the article) is that any particular reason comes with a certain level of relevant spatial resolution, which then allows you to determine a definite answer.

If you want to build a coastal barrier 10 feet in from the high water (or 1 mile out from the low-water mark) - the resulting elimination of fine detail makes the measurement comparatively simple. Basically, it's a question whose answer is entirely context dependent - trying to elimin

## Are Slashdot Editors Legitimate Nerds? (Score:2)

Because if they were, they'd realize that none of this is news to their readers.

## Ask Slartibartfast (Score:2)

He can give you an exact answer...

Its not 42.

## Norway (Score:2)

## Ruined maps (Score:2)

Let's not forget that the "weather maps" disagree with what is seen from space...

## Re: (Score:2)

...what?

## Now I have seen it all! (Score:2)

Now they sell us Geography 101 from last millennium as "news for nerds, stuff that matters."

I even almost RTFA before my brain awoke.

## It depends on who is President (Score:2)

## what about a curve? (Score:2)

## Re: (Score:2)

Coastlines are fractals, not curves. You cannot measure their length with calculus. Their length literally changes at the resolution you choose to measure them at.

## A fractal measurement challenge for you all. (Score:4, Interesting)

Read the article. It turns out that this is not a scientific journal or communique, not a technical report or abstract, not detailed information written by experts for experts. It is a general interest blog discussing items of scientific interest. It makes no claim to be novel or current. Furthermore, the article is not about the coastline per se. The second half of this very brief article discusses fractals and the relevant concepts about measuring length with respect to scale. While many people on Slashdot know this subject and its implications, many other people out there might not. So, as an informative article for laymen, it is perfectly reasonable for the forum it was published in. Even by those standards, it was still brief and naive, but if you have never encountered the concept before, it was a reasonable enough introduction to the idea. It does make one wonder though why it was posted on Slashdot, being as basic as it is.

However, the post has elicited many comments, and now, a challenge. For those who say the coast length is moot, well no, not really so. True, we can quibble the details, and the coastline is dynamic rather than static, and it all depends on length of your ruler. But that does not invalidate that the measure is important based on context. Examples:

- A boat is tasked to follow the coastline, maintaining a tangent or parallel course at all times, 200 meters of the shoreline. The boat has an aft screw, a certain length (e.g. 60 meters), and a certain rudder turning radius. Assume that the boat is laying cable and furthermore that it must to perform to perfect efficiency so that it can maximize the amount of cable it carries rather than excess fuel. How many kilometers will it ply, how many kilometers of cable are needed, how much fuel in its tanks?

- A coastal highway is being built 100 meters back from the high tide waterline. The road will be 10 meters wide. It will go from town A to town B, 20 kilometers from each other as the crow flies. Concrete and asphalt must be specified. How much of each are needed to complete the project?

- Recent seismic or volcanic activity has altered a coastline, creating a new large rocky mass along the coastline near an urban area. The altered contour creates new wave or current or tidal patterns that threaten erosion to coastline. How much rock, timber, concrete, or whatever will be needed to create a new seawall or jetty to protect human structures? Or, based on the metrics of those waves and tides, what will be the erosion rate along nearby beaches?

In each example, the length of the coastline has a tangible meaning. A rowboat that wants to follow the coast 10 meters away will have a different measure than an oil tanker following 2 kilometers away, but for the problems presented, their relative lengths matter. Based on the physical scales of each problem, the shorter rulers with longer coastlines, and the longer rulers measuring shorter coastlines must all be filtered out to yield the Goldilocks answer. As Obfuscant stated in a response above, "If you're estimating how much it will cost to install coastal protection you will measure how long the protection measure is, not how long the coast is behind it."

So, here is the challenge or invitation. Please respond below with realistic scenarios of a scientific, mathematical, engineering, or commercial nature where the length of the coast does matter for the problem or project at hand. They could be hypothetical or imagined, or they could be real world examples of prior endeavors or ordinary practices.

Post here . . . . . .

## Only one possible answer (Score:2)

## Spelling nitpick (Score:2)

## Roughness (Score:2)

## Does it include all the territories and islands? (Score:2)

As the title suggests, there are a lot of little places (Porto Rico, Hawaii, etc) that also add to the total, too.

Then, how far into a river do you track the coastline before it becomes riverbank?

Lots to consider. Little wonder there's differing opinions on it all.

## Always changing (Score:2)

In addition to the coastline being a fractal pattern, there is the fact that the coastline is constantly changing, at many levels. The tides go in and out, erosion deposits silt at the mouths of rivers, hurricanes wipe away beaches. Not only are coastlines un-measurable because of their complex shape, but because it's a moving target.

## Re: (Score:2)

You can travel billions of miles on the Earth's surface without revisiting any point.

## Re: (Score:2)

You can travel billions of miles on the Earth's surface without revisiting any point.

It's even worse than that, you can divide the earth's surface into a finite number of pieces and reassemble them to be two different earths each having the same surface area as the original earth..

https://en.wikipedia.org/wiki/... [wikipedia.org]

Then lather, rinse and repeat...

## Re: (Score:2)

They nailed it down the concept, but never provided a useful answer - other than the fact that for any well-formulated fractal the answer is likely "infinity".

## Re: (Score:2)

## Re: (Score:2)

Actually, it's exactly 5.72938473829. Determining the units is left as an exercise for the reader.

## Re: (Score:2)

Neither of those figures are the actual length of the coastline.