Lesson video

Hi, my name is Chloe, and I'm a geography field studies tutor.

This lesson is called Using OS maps to analyse physical features, and it's in the Geographical skills unit of work.

We're going to be looking in depth at contour lines, elevation, and how both of those things can help us to identify physical features.

Let's get started.

By the end of this lesson, you'll be able to use contour lines to identify and describe physical features on a map.

There are some key words we need to think about first of all.

The first one is relief, and this very simply is the shape of the land.

Then we have contour lines.

These are lines on a map that join points of the same height.

A spot height is a point marked on a map showing a particular height.

This lesson is in three parts.

So first of all, we're going to think about how is height shown on a map.

We will then look at how do contour lines describe gradient.

And then we look at how contour lines describe features.

So relief, as I said, is the shape of the land.

It refers to two different ideas.

First of all, elevation, how high a point is above sea level, and then gradient, which is the angle of the land.

Cartographers, people who make maps, use different methods to show geographers the relief of an area.

So one way they show elevation is through think something called a spot height.

So this states the exact height of that point above sea level.

Some spot heights have been calculated from the air using drones.

They have lasers which measure the distance between the land and the drone.

And this is a form of remote sensing called LIDAR which stands for laser imaging, detection, and ranging.

Spot heights written in orange have been calculated from the air, while those in black have been calculated from the land.

And you can see in our example here we have two spot heights.

71 is written in orange and you can see the little dot next to the seven there.

And 63 is written in black and the little dot is actually on the road there.

So you can see those spot heights quite clearly on an OS map.

Triangulation pillars, you might hear them also called trig points, are stone or concrete posts.

You can see one in the picture there.

They're usually found on top of mountains or on top of significant peaks.

These also show elevation on a map.

And the symbol for a triangulation pillar is a blue triangle with a blue dot in the centre.

The elevation in metres will also be written next to it, and you can see one in the map extract here, 734 metres above sea level.

So let's check our understanding so far.

Which symbol has been used to show an elevation of 527 metres? Have a look at the map extract there.

Let's have a look at our options as well.

Is it A, a spot height, B, a triangulation pillar, C, LIDAR, or D, relief lines? Pause the video now and have a good look at the map and then tell me your answer.

Right, let's take a look.

Hopefully you got that one right.

Yes, it is a spot height.

You can see it down towards the southeast corner of the map extract there in orange, 527 metres.

Another way of showing elevation on a map is to use contour lines.

These appear as thin, orange, or brown lines with elevation in metres marked on them.

Contour lines join places that have the same elevation.

Reading contour lines helps geographers to visualise what the landscape is like.

So in areas where contour lines appear close together, or in urban areas, some numbers may have actually been removed from the contour lines to reduce the visual clutter on the map.

If you have a look at the map extract that's on the right hand side there, you can see there's an awful lot of contour lines.

And if all of those were marked in figures with their elevation, that should be so much information on the map, it would be more difficult to read.

So the contour interval, this is the difference between the contour lines in elevation.

It can be maybe five or 10 metres if the area is quite flat.

So if we look to our map extract on the left there, you can see that the contour interval there is 5 metres.

So it's going from 25, 30, 35 to 40.

Or it can be up to 100 metres if it's really hilly.

In our other map extract, you can see we've got a contour interval of 10, but only every 50 are marked.

Every fourth or fifth line is thicker, and this is known as an index contour.

And again, if you look carefully at the map extract on the right, you can see that every fifth line is actually a bit thicker than the other ones around it.

So it just is a little visual clue to help geographers read the contour lines.

So let's check our understanding of that point.

True or false? All contour lines have the elevation marked on them.

Pause the video and have a think and then tell me if that is true or false.

Hopefully you realise that that is false, but why is that statement false? Well, well done if you mentioned that contour lines, because they sometimes sit quite close together, it may be that the elevation values have actually been removed by the map makers so that the map does not become cluttered with symbols and makes it easier to read.

So our first practise task of this lesson, you can see we've got the map extract we saw earlier, but now we've got four additional letters on there, A, B, C, D.

Our first part of this task, what are the elevations of each of the letters A, B, and C on the map? And then the second part, I would like you to estimate the elevation of point D on the map.

So use the contour lines to help you work out the height of the land at each of those four points.

Pause the video.

You might wanna have a chat with a friend and see what they think, and then come back to me.

Right, let's see what you got.

So for A, 25 metres, it's sitting right on the line, so we know it's got to be that.

B is sitting on the 35 metres line.

It takes a little bit of working out because the 35 value is actually written quite high up in the square, and so then you have to follow the line down to where B is.

C, it's not a contour line at all, but it is a spot height.

So well done if you recognise that.

And it is 39 metres.

Then the second part was estimating the elevation of point D.

So D seems to be sitting in the middle of nowhere, but if we look, it's actually sitting between the contour line for 30 metres and the contour line for 35 metres.

So we know it's got to be between those two points.

But because it's sitting quite a bit closer to the 30 line than the 35, it's only gonna be slightly more than that.

So 31 metres is what I've said.

Hopefully you got that right.

Now, let's move on to our second part, how do contour lines describe gradient? So here's an example for you to think about.

Aisha is walking from point A to B on the map.

So you can see she's going to be walking through a variety of different contour lines there.

Will she be walking uphill or downhill? Well, if we look at the values on our contour lines, we can see that they go up in number between A and B.

And this means that as Aisha walks, she will be walking across land of increasing elevation.

And this means she's gonna be going uphill.

So she's starting just below the 115 metre mark, and she's rising up to, let's have a look, 175, 80, 85, nearly 190 maybe metres in height there.

So she's actually going uphill on that walk.

So plotting a route on a map and then reading the contour lines can tell geographers a lot about what their journey will be like.

Let's look at what the route that Aisha is taking now.

So she's still going from A to B.

She starts just below the 10 metre line this time and then she goes up 10, 20, 30.

She's then dropping down again to 20.

Then she's got a section where there's no contour lines.

Then she crosses another 20 line, and then she's going up 30, 40.

So on this journey, Aisha climbs a hill, goes down the other side, then when there's no contour lines, that's where we are thinking that she'd be walking along a flat area or relatively flat before climbing the hill again.

So it tells us an awful lot about what her journey's going to be like just by reading the contour lines.

Let's check our understanding of those ideas.

Complete the sentences with the missing words.

You're definitely gonna want to pause the video here.

Have a good look at the paragraph and see if you can find the missing words.

Right, what did you get? Let's check.

As one moves across the map, the elevation marked on the contour lines will change.

If the values increase along the route, the person will be travelling uphill, while if the values decrease, they will be going downhill.

Hopefully you got that correct.

The distance between contour lines tells us a lot about the gradient of the land.

So let's look at Aisha's route now between A and B.

She's starting below 10 and then she's going up to an elevation of 40 metres.

If the contour lines are close together as they are in this picture, Aisha will reach 40 metres in elevation after only a short distance.

She has gotta travel very far.

Although she'll be going uphill, it will be only a short distance, and this means the gradient will be steep or sharp.

But if the contour lines are far apart, and you can see they've really spread out now, she's still going to reach 40 metres in elevation, but she's gonna have to walk a lot further in order to reach that.

So that means the gradient's going to be fairly shallow or gentle.

Which part of the map here shows the steepest gradient? So remember, the closer the control lines are together, the steeper the land is going to be.

Have a good look at the map extract and then come back to me with whether it is A, B, or C.

So let's look at each of our options.

Well, first of all, A, yeah, we can see there's some big gaps between the contour lines there, so we know although it is showing a slope, it's a fairly gentle one.

C is showing the top of the hill at 147 metres.

Yes, the contour lines are closer together than they are at A, but they're not the steepest.

The correct answer is B.

If you actually look at B, the contour lines are so close together, it almost looks like that entire section has been shaded orange, but if you look closely, you can see they are individual lines.

Because it's next to the C, we have to assume that that is a cliff, probably the steepest part of our physical landscape.

Let's look at our second practise task.

Our first part here describe Aisha's walking route between point A and point B.

You can see she's got a bit of variety in her walk.

You should describe whether she's going uphill or downhill, and you should also describe how the gradient changes as she walks.

So from A to B, what is her route going to be like? Then use a paper or a digital OS map and plot a route between two points of your choice.

It can be completely random, but I'd like you to choose a route that's roughly 2 kilometres long.

Describe what your journey will be like if you moved between those points.

Make sure you include information about whether you're going uphill, whether you're going downhill, maybe you're going across a flat area.

And also describe what the gradient of the land would be like.

Choose somewhere that's more rural so you could be able to see the control lines a little more easily.

You're definitely going to need to pause the video here.

Do have a go at those two tasks and then come back to me.

Let's look at Aisha's walking route between A and B.

There's a few different ways you could write this, but you need to make sure you've included these points.

First of all, that she's going downhill and that first downhill is a gentle slope.

You can then see she's not going across any contour lines for a short section, so we know she's going to be crossing some flatter land.

She's then going to be going uphill, and when she goes uphill, it's going to be a steep gradient.

You can see that because the contour lines are closed together.

Then we have your journey that you are taking between two points.

You need to make sure your answer includes a description of whether you are moving uphill or downhill in different sections of the journey.

And you'd also need to include description of the gradient, whether it is steep, gentle, or flat.

Do check your answer carefully to make sure you've included those points.

And now we're moving on to the third part of this lesson, how do contour lines describe certain features? So the landscape is made up of a number of physical features, and there's actually more than I could include in this lesson here, but I've included the main ones for you to be able to recognise.

It is all about looking at the contour lines and recognising particular patterns about how they're laid out, and particularly whether there are areas of flat land, steep land, or gentle land.

The most straightforward feature for geographers to identify is a plain.

You might be thinking about a floodplain if you had a river running through the middle of it.

In this area, it's really flat.

There'll be almost no contour lines at all.

You can see towards the edges here we've got some 10 metre areas, but otherwise the section in the middle, completely flat.

Then we've got a plateau.

So this is a flat area on top of a hill.

So the contour lines will increase in value, and it could be steep or it could be gentle.

And then when they get to the top, there'll be no contour lines at all.

So there'll be an area of no contour lines almost at the top of the hill.

So you can see here, 10, 20, 30, 40 and then it stops.

There's no contour lines after that point.

So we know we're at the top of the hill and it's fairly flat at the top.

Then we've got a knoll.

A knoll is what we would refer to as an isolated hill.

You can see it kind of sits on its own in the map on our extract there.

This means that contour lines increase in value up to a peak and then immediately come back down again.

If you were to look at it in the landscape, it would be literally like this.

So the contour lines would be going up one way and then coming straight back down the other side.

A ridge is a long thin hill and it often has very steep sides.

The contour lines are close together along the long sides, and you can see that in the image there.

And then they're further apart at the ends.

So there can be really like a knife edge kind of feature in the landscape.

Then we've got escarpment.

And escarpment is a hill with one steep side and one gentle slope.

These can be quite difficult to find on OS maps because they're often in amongst a variety of other hills.

So you can see in our diagram here, the contour lines are close together on one side, so more on the westerly side of this escarpment they're close together, and then as we go up to the top of the hill, we've got a small plateau, but then they gently fall away on the other side.

So one steep side and one gentle side to our escarpment.

Let's check our understanding of those features so far.

What is the main difference between a plateau and a knoll? A plateau is higher in elevation.

A plateau is lower in elevation.

A plateau has a flattened top.

Or a plateau has a peaked top.

Think back to my different descriptions there, the different features, and decide which one of those is correct.

Hopefully you recognise that a plateau is a hill with a flattened top, whereas a knoll is the one with the peaked top.

Now, valley and spurs, these can be quite easy to confuse on OS maps, even more so because they often appear right next to each other.

What do you notice is different between the different contour patterns? Look closely at what's going on in these pictures.

So well done if you recognise that the contour values seem to be kind of be working in opposite directions.

We've got 40 to 10 in one direction and then in the other picture it goes from 10 to 40.

And this isn't a mistake.

This is very intentional.

A V-shaped valley is a V-shaped bowl.

The lowest land is in the centre with higher sides reaching up around it.

Contours are shaped like Vs with the highest value elevation on the largest V.

Let's take a look at our picture here.

You can see, the biggest V in that picture is the 40 and the smallest V is the 10.

We can also see we've now got a river running through the middle, and this is very common when you have a valley, that you will have the path of a river running straight through the middle.

Now, a spur on the other hand, same shape, but different numbers.

So the spur is like a V-shaped finger of land.

Contours are still shaped like these, but the highest value is on the smallest V.

So the numbers are in the opposite direction.

Let's take a look at some real maps now.

Which map detail shows a spur? Is it A, B, C, or D? You're definitely gonna want to pause the video here.

Have a really good look at each of these.

And this is not easy at all, so do take your time and then come back to me.

So well done if you've got this.

Yeah, it's B.

That is our spur, that kind of finger of land.

Before we look at B, let's look at our other pictures here.

So A, I would say this is a knoll.

We have our contours going up to a peak and then they're coming straight back down the other side.

Now, C, it is a kind of V-shaped system of contours and we've got a clue here in that there's a river running through the middle of it, so yeah, that is a valley.

So well done if you spotted that as well.

D, we've got barely any contours and where they are.

They're very far apart.

So well done, again, if you notice this was gonna be a plain and particularly a floodplain 'cause we can see we've got the river running through the centre.

But B, we've definitely got some kind of V-shaped, possibly more U-shaped contours here.

They are very steep on their sides, and you can see that they are going from the highest in the middle to the lowest value on the largest contours further out.

Well done if you spotted that.

Our final task of today, write the letters in the correct place on the map to show the location of each of the features.

So we've got seven features there for you to try and identify on the map.

Now, there are more than one of some of these, so it might be that you'll see that there is maybe a valley in one place, but there also a valley somewhere else as well.

So maybe you could mark your letters more than once if you spot them.

Do pause the video and have a really good look at your diagram there and see if you can get the letters in the right place.

Right, let's look at your answers.

So first of all, we've got our plain A.

So long as there aren't any contour lines anywhere near them, you can put your A anywhere like that.

So I've put mine here.

You might also place it more towards the top left corner of the map as well.

That is part of the plain as well.

But anywhere like that.

Now, a plateau, we've gotta remember that is our flat topped hill.

So we've got one towards the western side of our map and one towards the eastern side.

Our knoll is that there's only one that you could get for this one.

It has to be that one.

It's an isolated hill, so it's sitting way out from all the rest of the contours.

Our ridge, we are looking for a long thin structure.

So well done if you noticed that our ridge is in the bottom right hand corner there.

Our escarpment is over here.

We have one side of the hill having steep lines, and then on the other side the contour lines are further apart, indicating a more gentle slope.

Our valleys, I've marked two of them.

You could keep going then, be even more detailed and have a third one, but those are the two main ones.

And yes, it has got the river running through the centre.

And then finally, we've got a number of spurs as well.

So you can see I've marked on those, and actually there's a spur in between the two valleys, so you might have found that one as well.

Well done if you managed to get all of those.

It is not easy, and it does take quite a lot of practise to get to learn how to read contour lines.

Let's look at the summary of today's lesson.

Relief refers to both the elevation of points and the gradient of slopes present in a landscape.

Elevation can be shown on a map through the use of a spot height, triangulation point, or contour lines.

Gradient can be shown by the relative position of contour lines.

And lines that are close together show steep gradients.

Those that are further apart show slopes that are gentler.

Well done.

There was a lot of technical information in that lesson, wasn't there? If you want to practise your contour line reading, do get out an OS map.

It's almost like learning another language, learning to recognise those patterns within the contours and therefore finding the features.