Original subtitles

Map scale is at the same time kind of a straightforward idea, but also there's

a few little details that I think are important for us to elaborate on.

So let's talk a little bit about map scale.

The purpose of map scale is just to show distances on a map.

If I'm looking at a map, and especially if it's an area I'm not familiar with,

it's really hard sometimes to get a sense of how far is it from a to b?

Is that a few blocks?

Is it a kilometer?

Is it really far?

So that's the whole purpose of map scale, is to indicate to somebody distance.

On this slide here,

I'm showing three different map areas that are all the same size.

In other words, the squares on the slide are the same size, and yet

they're showing very different sized areas.

So the distance from here to here is very different on

the ground than the distance from here to here on this map.

Which of course is very different than the distance on this map again.

So even though the size of the squares is the same, the distance is quite different.

So how do we tell people what those distances are?

We use a map scale.

So what would be the walking distance to get from point A to point B?

If we're looking at this map and I want to know, this is in London, England,

near Buckingham Palace.

If I want to know, well, how far is it from this point to that point, for

whatever reason, how would I calculate that?

How would I figure that out if I needed to?

So the map scale is needed to calculate that distance.

So scale is represented as a ratio of the map distance to the ground distance.

It's expressed as 1 over a number.

The numerator is always 1, the denominator can be any number, really.

So we have a ratio of map distance to ground distance and

the scale is always 1 to something, that's the way we would say it.

So in this case, 1 to 250,000.

And the important thing too here is that there are no units to a math scale.

As long as the units are the same for both the numerator and the denominator.

And what I mean by that is if we said that, whatever,

this is 1 foot to 250,000 feet.

That would mean that if I measured 1 foot on the map,

that would equal 250,000 feet on the ground in reality.

But I could just as easily had said 1 meter on the map equals 1 meter on

the ground, or 1 centimeter on the map is 1 centimeter on the ground.

Or 1 cubit, or fingernail, or whatever, it could be any units you want.

The point is, as long as they're the same, that's the important part.

And people get tripped up on this all the time because especially if it's

something like centimeters, then the denominator is centimeters as well.

You can then convert the distance that you've calculated into meters,

or kilometers, or something else.

But when you first calculate it will be in the same units that the map scale is that

you measured it from.

So on a map you probably are going to measure, say if it was a paper map,

the distance across that paper map in centimeters, not in kilometers, and

then you could calculate the distance on the ground.

And that then would make more sense to convert it to some unit that's more

relatable, like kilometers.

Okay, so if we measure the map distance from A to B here as being 10 centimeters.

So, in other words if it was 10 centimeters on a paper map or

it's 10 centimeters on this screen.

Doesn't really matter, as long as we know what this scale is and we know

what the distance is on the map, we can then calculate the distance on the ground.

So let's do that.

So 10 centimeters on our map, if this map was at a scale of 1 to 5,000,

that means that 10 centimeters on the map is something on the ground.

So we're going to solve for x,

we're going to do a little cross multiplying here.

So x = 10 cm x 5,000, so essentially, really, we're taking this and

we're doing cross multiplying, that's what we have there.

And so we multiply those together, and so the actual distance is 50,000 centimeters,

and then if we wanted we could convert that to something more useful,

like meters, like 500 meters, okay?

That's all there is to it.

It is useful to know how to do,

some people are more mathematically inclined than others, but

I think most people should to be able to figure something like this out.

And it's just a useful thing to be able to know how to calculate.

There are three main ways that we can express a scale on a map.

We can do it as a representative fraction.

So that would be as a ratio like this, 1 to 500,000.

Sometimes this is also referred to as an absolute scale,

you may see that in the software that way.

Sometimes it's indicated as a verbal scale,

especially on maps with imperial units like in the United States.

A common scale might be something like one inch to a mile.

So 1 inch on the map is 1 mile on the ground.

Now, that's kind of doing a unit conversion as part of the way the scale's

being expressed, which may be more or less confusing.

But maybe that's why metric's a little easier to work with,

just saying, as a Canadian, a little editorial there.

[LAUGH] And we can also represent it as a bar scale.

So depending on the scale of the map that you're making,

one or more of these might be more or less useful.

So when should you use each of these?

It's a good idea to include a representative fraction on virtually any

map that you make.

You can't really go wrong with that.

So at the very least I would include a representative fraction.

A verbal scale is really only useful for unusual map scales, like I said,

like imperial units in the US,

so in that case certainly that would make sense to include.

A bar scale is visually easy for people to understand, it's quite useful.

And as we'll see in later section though, there are maps of certain scales and

projections where a bar scale doesn't really make sense,

like the Mercator projection, for example.

So there's a kind of a rule of thumb that people often will use, or a convention,

is that a bar scale only makes sense at a larger map scale than say 1 to 250000.

And larger map scale means actually zoomed in, as we'll talk about it in a minute.

But smaller map scale means zoomed out, if you want.

So if you have a map, say, of a state, or province, or a country, or

the world, a scale bar is really not the most useful way to represent scale.

I would probably just go with a representative fraction.

Okay, let's talk a little bit about terminology.

If I show you a map of the world and I ask you, is this a large scale map or

a small scale map?

And you're probably thinking already this must be some kind of trick question.

And yeah, it kind of is.

It's a small scale map.

Now, this is one of those pedantic little details that cartographers and

GIS people pay attention to.

Is that this is where the confusion comes from, is that if you said you were working

on a project that was in 20 different countries, and it's a worldwide effort,

and it's a big project.

In everyday normal language you would call that a large scale project,

but it's not a large scale map.

If you make a map of the world it's actually a small map scale.

And if you were making a map of say a neighborhood,

that might seem like a much smaller project, but it's a much larger map scale.

So why is it like this?

Why do we insist on being different like this?

Well, let me explain.

Here we have five different maps that are all the same size on the screen.

The squares are all the same size,

but they're representing different sized areas, so they're different map scales.

They actually range from a large scale to a small scale.

So the large scale would be something with a representative fraction of,

say, 1 to 5,000 versus a small scale map which would be, say, 1 to 3 million.

So this is a map of really just one individual building,

this is actually Buckingham Palace.

Versus at the other end of the spectrum, let's say, is a map of the entire world.

So where does this confusing terminology come from?

It's from these numbers, 1 over 5,000 is actually

a larger number than 1 over 300 million, okay?

If we convert that to decimals, then this is 0.0002 and

this is 0.000000003333, okay?

So it's actually a much smaller number if you divided them,

and that's where that terminology comes from.

Is that this is a larger number, therefore, it's a larger map scale.

This is a smaller number, therefore, this is a smaller map scale.

And that's the way I try to avoid confusion with people.

Well maybe I'm being pedantic, but it's not like I'm going,

excuse me, I think you used that terminology incorrectly.

I'm just trying to say, you mean a large map scale or something.

I try to be polite about it, but sometimes all you're trying to do is,

not that I'm trying to make somebody feel bad,

I just want to make sure we're talking about the same thing.

That's really what it comes down to.

So really you can think of it as a continuum of map scales.

Sometimes I get asked well, so what's the cut off?

When does a map suddenly become large map scale versus small map scale?

I don't know that there really is a hard and fast rule about this.

I tend to think of it like, if you're looking at a neighborhood, certainly

that's a large scale or, I don't know, a few neighborhoods would be a large scale.

A city would be kind of medium scale, a state or province would be small scale,

and certainly a country or the world would be small scale.

So it's not a trick question or

something it's just kind of a relative term that gets used.

And so I think after a while the more you make maps and

the more you talk about them you kind of get a sense of what the correct range

of scales would be in terms of the terminology.