Lesson video

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

This lesson is called Using OS maps to locate places.

It forms part of the Geographical skills unit of work.

We're gonna be covering lots of different ideas around how to use OS maps effectively.

So let's get started.

By the end of this lesson, you will be able to use directions, grid references, and scale to find precise locations and distances on a map.

There are a few keywords we need to think about.

So first of all, cardinal points.

You will know these even if you might not know the term.

They're the four main compass points, north, south, east, and west.

An easting is a vertical line running north to south on a map that divides it into east and west parts.

A northing is a horizontal line running west to east on a map that divides it into north and south parts.

This lesson is structured in three parts.

Let's have a look at those now.

The first part, how do geographers describe direction on a map? Secondly, how do geographers use grid references on a map? And then finally, how do geographers use scale on a map? So let's start with that one about direction.

So directions can be described to differing amounts of detail.

First of all, the least accurate is where geographers most commonly use the cardinal points, so the north, south, east, and west points.

We've then got the ones in between those, and these are called the intercardinal points.

So northeast, southeast, southwest, and northwest.

If you want to be even more precise, a geographer might use the secondary intercardinal points.

So you can see that between north and northeast there is north-northeast.

Between west and northwest, there's west-northwest.

So they form in between the cardinal points and the intercardinal points.

OS maps always align so that grid north is at the top of the map.

And grid north is the direction of north if one were to view the world as a 2D map rather than as a spherical globe.

You could argue therefore that grid north only really exists on a map.

From any point on the Earth's surface, true north points towards the North Pole.

So it's slightly misaligned from grid north, 'cause remember, we are talking now about the world as a sphere rather than as a flat surface.

Then there's magnetic north.

Now, a compass will always align with the Earth's magnetic pole and that's constantly moving.

At the moment, it's moving from west to east across the UK.

And this is known as the magnetic north direction.

So there's actually three different ways of saying where north is.

As geographers looking at OS maps, we're going to be thinking mostly about grid north.

So true or false? An OS map is always aligned so that the top of the map is true north.

Is this true or is it false? Pause the video and have a think, and then I'll tell you the answer in a moment.

Well, I hope you recognise that that answer is false, but why is it false? Yes, it's not true north that the OS map is lined with.

It's grid north.

It's really important to remember that because grid north represents the idea of a flat surface, nothing to do with the spherical shape of the world.

Geographers might use bearings to describe direction more precisely.

So bearings are measured in 360 degrees, starting from 0, the north point, and then moving clockwise around the compass points.

So Laura here has worked out the bearings of the other cardinal points.

You can see if north is 0 degrees, east is going to be 90, south is 180, and west is 270 degrees.

What are the bearings of the intercardinal points then? We can see we're gonna have to do a little bit of maths here to work these out.

First of all, there's gonna be 45 degrees between 0 and 90.

So this is going to be northeast.

Southeast is at 135, southwest at 225, and northwest at 315.

You can see they're exactly the same amount apart and it all adds up to 360 degrees.

So to work out the bearings from a map, geographers have to use a protractor.

The centre of the protractor is placed on the starting point.

And in this example, A is my starting point.

And you can see there the centre of the protractor is dead centre on the location A.

0 degrees on the protractor has to be aligned with grid north.

And you can see we've got grid north on the map just to help us out.

And you can see that the protractor is aligned in that way.

Geographers can then read off the degrees that align with the position of the finishing location.

So in this case, it's B.

So what I would do is draw a line between A and B, either if a real or imaginary line, and then I would be able to read off on my protractor how much the bearing is at that point.

And we can see that B is on a bearing of 120 degrees from A.

Now, it's really important here that we remember that A is not on a bearing of 120 degrees from B.

To work that out, we'd have to move our protractor, so the centre of the protractor is now on B, and then we would do the same process to then find out the bearing towards A.

It's only from A to B that the bearing is 120 degrees.

Let's check our understanding of those ideas.

Complete the sentences with the missing words.

I'd recommend you pause the video now so that you can have a good look at the paragraph and then decide on what words you're putting in the blank spaces.

So bearings allow a geographer to measure direction more accurately.

You might have used precisely or a word that means the same thing.

They're measured in degrees, 0 degrees to 360 degrees.

To work out the bearings between two places on a map, geographers use a protractor.

Hope you got those.

Now, our first task of this lesson, complete the table by working out the compass points and bearings of the straight line route between the features on the map.

That's gonna appear on the next slide.

The compass directions might be cardinal, intercardinal, or secondary intercardinal points.

So let's take a look at our map.

It's a fairly simple one.

We've got three locations, A, B, and C.

But remember what I said about it really does depend on what our starting and finishing location is as to what bearing we're going to be taking.

So first of all from A to B, then from B to C, and then from C to A, tell me what the compass direction is and then work out the bearing between those points as well.

Pause the video, this will take a little bit of time, and also double check your answers quite carefully before you press play again.

Let's look at your answers.

So from A to B, it is a northeast direction, and that's a bearing of 45 degrees.

From B to C, you can see the angle is quite different there, south-southeast is quite acute, and that is 157.

5 degrees.

Then from C to A, it's directly west, so it's 270 degrees.

So we've used cardinal, intercardinal, and secondary intercardinal points in our answer there.

So I hope you managed to get those.

Let's look at the second part of our lesson now, which is going to be thinking about grid references.

The Ordnance Survey and Ordnance Survey Northern Ireland are organisations that are responsible for mapping the whole of the UK.

And the UK is divided into 100 kilometre by 100 kilometre squares and each has a two letter label assigned to it.

And this is known as the OS national grid.

You can see it in the image there.

It is really important to remember it does not align with international latitude and longitude lines.

Those, again, are more to do with the Earth when we think of it as a sphere rather than a flat surface.

Each OS map will refer to this two letter label so the reader will know which part of the UK they are looking at.

So you might already be able to see where you are in the UK and be able to work out your two letter code.

OS maps have grid lines drawn on them that divide the map into a number of smaller squares.

And you can see an example of one of those squares here.

The grid lines that run north to south are called eastings.

The grid lines that run west to east are called northings.

And you can see that these grid lines on the map are represented by very thin blue lines.

All eastings and northings are placed on the OS map so that they are the equivalent of 1 kilometre apart in real life, so 1 kilometre between the each easting and 1 kilometre between each pair of northings.

Each easting and northing will have a two figure value from 00 to 99.

The most westerly easting in an OS national grid square will have the value 00.

You can see that on the image there.

And the most easterly will have the value 99.

Now, if you look closely, you can see that the 99 value is not actually on the line itself, it's just inside it.

And the reason for that is that if it was on the line, it would be incorrect.

The line is 00 for the next square to the east.

So the 99 has to sit just inside that line.

The most southerly northing in an OS grid square will have the value 00 and the most northerly will have the value 99.

And again, you can see the 99 is sitting just inside the square because if it was on the line, it would be the 00 for the next square north.

It's these values that give us the numbers that form part of grid references.

This means that there are many areas of the UK that will have the same four or six figure grid references because the same 00 to 99 values are repeated for each square in the OS national grid.

So you can see here in our picture, we've got the square which is denoted SH will have a 09 14 and the square next to it will also have a 09 14.

So across the UK, there are lots and lots of 09 14s.

So let's check our understanding of that.

True or false? A four figure grid reference will be unique for a particular place in the UK.

Is that true or false? Pause the video and come back to me.

Well done if you recognise that that is false, but why is it false? Well, a four figure grid reference will be unique for the national grid square, but of course there are lots of national grid squares that cover the UK.

There's gonna be lots of four figure grid references that are the same.

To find a four figure grid reference for a feature on an OS map, one first locates the grid square in which it is found.

The four figure grid reference is the value of the easting and the northing that cross at the bottom left corner of the grid square.

So let's take a look at our example for this.

You can see that our easting is 90 and our northing is 50.

So where those cross is at the bottom left there so we know we're dealing with those numbers rather than the 91 and the 51, which also appear in our grid square.

Very important to note that the easting is always written first out of the two.

Jun wishes to find the four figure grid reference of Mount Castle Farm.

He's located it in this grid square.

So let's take a look.

There it is.

It's in the eastern side of the square.

So in this case, the easting is 90 or 90, the northing is 50 or 50, and that puts it together as 9050 for the four figure grid reference from Mount Castle Farm.

And do note how I said that 9050.

That's how you would say it.

Not 9050.

Now we will find the six figure grid reference for the farm.

So this six figure grid reference is much more precise.

This tells the geographer where a feature is found within that 1 kilometre by 1 kilometre square.

So let's take a look at our eastings first of all 'cause that's the one thing we're going to be writing first.

We've got our 90 that we have from our four figure grid reference.

And then what we do is work out how far east into the grid square the feature is found.

So it's like we're imaginary lining our grid square into tenths so we can count how many tenths into the grid square our farm is found.

So we're on 90, one, two, three, four, five, six, seven, eight, nine, so that means our next figure is going to be 9.

Then we need to be thinking about the northing value.

So again, we've got our 50, so that comes next.

And then the final number indicates how far north into the grid square the feature is found.

And this is also measured in tenths.

So we've got our 50, and then it's one, two, three, four, so our final figure 4 goes in there.

So this means the six figure grid reference for Mount Castle farm is 909504.

And again, note how I've said that.

I've used each number individually rather than trying to call it 909504.

I think you can now see why geographers have to use it as six separate figures so it avoids any confusion.

Let's check our understanding there.

What is the six figure grid reference for the public telephone in Wickham? And you can see the symbol there we're looking for.

It's a black handset phone.

You can see it's pretty much just north of the centre of the square.

Let's look at our options.

404724, 396717, or 404717.

This definitely will need you to pause the video.

So do so.

Take your time, be accurate, think about all the rules about how you write a six figure grid reference, then come back to me hopefully with the right answer.

Right, let's see which one is correct.

It's, yes, 396717.

We can isolate our easting as 39 and our main northing as 71.

And then we are saying it is six tenths to the east of the 39 line and it's seven tenths to the north of the 71 line.

Let's now use our tasks to practise those skills a little more.

Find the six figure grid references for the following features.

First of all, the campsite and then the carpark.

And you can see we've got the symbols there to help us find them on the map extract.

Using the same extract, then find the feature located at the following grid references.

So you've got 252176 and 257170.

Now, you'll definitely have to pause the video to have a go at this.

Try to be as accurate as possible, and I'll tell you what I think the answers are.

Right, first of all, the campsite, you can see it is there more towards the midwest of the square.

Our six figure grid reference should be 253175.

Now, you should definitely have the 25 and the 17 correct.

If you are one out on the others, I will accept it.

So you could have, for example, 252174, for example.

I would say is fine 'cause probably you're going to be doing this by eye.

Let's look at the car park as well, 257173.

So 257, you can see we're further to the east into the square, so our tenths have gone up, and 173, we are lower than the campsites.

We know we're going to be less than the figure we had before.

Hope you got those right.

Then we've got the features that are found at these grid references.

So we've got 252176, and you can see we have a school just along the edge of the yellow road there, and then 257170, it is a Ford.

And if you actually look, this is one of the trickery that you have to be mindful of with OS maps.

The name Ford, the label Ford is not where the actual Ford is.

The Ford is where a river crosses a path.

So the actual Ford is pretty much on the 170 line.

So just be careful of that, that you're not just looking at the label of the feature, you are looking at the feature itself and where that is.

Right, we're moving on to the final part of today's lesson, how do geographers use scale on a map? Now, OS maps are described using a ratio scale.

So that's normally 1 to 25,000 or 1 to 50,000.

Those are the most common maps that we use.

A scale of 1 to 25,000 means that every 1 centimetre on the map is the equivalent of 25,000 centimetres in real life.

What this means is, if we think about our maps here, 4 centimetres on a map is the same as four lots of 25,000 centimetres, in other words, 100,000 centimetres.

Now, we can't work in those kind of units, so let's scale it down.

We could be talking about 1,000 metres or more commonly 1 kilometre.

So 4 centimetres on a map means 1 kilometre in real life.

And that's a nice figure to keep in mind as you're using OS maps more frequently.

This calculation will vary slightly depending on the ratio scale.

The same principles apply, but you'll just have to be thinking more carefully about the numbers you are using.

OS maps also have a scale bar.

It will look something a little bit like this.

This is useful for measuring distances between two features on a map, and this might be a straight line distance or it might be a curved distance.

So let's say you are wanting to measure a straight line distance.

What we do is we find our two points and then we use a ruler to measure in millimetres or centimetres the distance between the features.

So in this case, you can see we've got two features that are along the coastline.

We're going to be using our ruler.

Pop it in place.

We can read off, in this case, it's millimetres, we're going to be using 65 millimetres.

What we then do is place our ruler along the scale bar, and we can read off the real distance from the distance that was measured.

So we put it on the scale bar 65 millimetres and we've got 1.

6 kilometres.

Let's check our ideas there.

Alex has measured the straight line distance between the sewage works and Chapel Farm.

So we're back to our grid square that we saw a moment ago.

You can see Chapel Farm is in the middle and the sewage works is towards the north of the square.

So we're using our ruler to measure the distance between those.

We then place our ruler alongside the scale bar, but what is the distance between the two? Is it 0.

5 kilometres, 1 kilometre, or 2 kilometres? Now, pause the video if you have to to look carefully at the ruler and its position on the scale bar, and then come back to me with the right answer.

Right, so hopefully you can see that the ruler that's sitting on the map, the distance between Chapel Farm and the sewage works is a touch over 2 centimetres.

And then if I look at my ruler that's on my scale bar, I can see that 2 centimetres is 0.

5 kilometres.

So my answer A is the correct answer.

Now, what about if we want to go around a curve? So this time to measure a curve line distance, you use a piece of paper and you place the straight edge of the piece of paper, so that one end is next to the kind of starting feature, if you like.

So you can see here in the animation, we are now measuring the same distance that we're measuring before, but we're now going around the edge of the headland.

So we place our piece of paper at the point where we're starting our measurement.

We then mark that starting point with an X.

So we need to have that really clearly marked on our piece of paper.

What we then do is we pivot our paper around the coastline, and every time we need to pivot, we make a mark on the piece of paper, and you can see we're curving around the headland there until we have a distance marked on our sheet.

So pivot the paper at X so that it follows the curves of the path.

And each time the paper is pivoted, you're making a new mark on the piece of paper, and that then becomes your next pivot point.

What you then do, just like you did with your ruler, you now place your piece of paper against your scale bar and you make sure that the X that you made at the start is alongside the zero value, and then you can then just read off the distance in real life.

So Jacob is measuring the curved line distance between two features.

He's already done that and he is got his piece of paper ready to read on the scale bar.

He's placed it against the scale bar, but what mistake has he made? Jacob is saying that, "In real life, the distance is 3 kilometres." Hmm, is it? Is the mistake he's made that he needs to measure his paper using a ruler? Is it that the X does not line up with the 0 on the scale bar? Or has he not made enough pivot marks on the paper? Pause the video and have a think about this, bearing in mind everything we've just discussed, and then come back to me.

Well, I hope you can see here what Jacob has done.

Yeah, the X is not aligned with the 0.

So although his final mark is lying next to the 3 kilometre point, he hasn't started his piece of paper in the right place.

So he needs to shift it back so that the X is in line with the 0.

Our final couple of tasks for the day.

So for each of the scale ratios in the table, work out the real life distance in kilometres for the map distances shown.

So, for example, if you've got a ratio scale of 1 to 10,000 and the distance on the map is 2 centimetres, what will be the distance in real life? So remember, if it's a 1 to 10,000 scale, it means that 1 centimetre is the equivalent of 10,000 centimetres in real life.

So some maths needed for those.

You've got three different figures to work out.

Then I'd like you to use an OS map to practise measuring curved distances between two features.

So you'll need a bit of scrap paper as well.

Note down any checks you make to ensure that your measurements are as accurate as possible.

What are the things that you're doing mentally to actually make sure that that distance you are measuring is as true as possible? Do pause the video to have a go at those tasks and then come back to me with your ideas.

Let's take a look at your answers.

So we had to do a little bit of maths here to work things out.

On our 1 to 10,000 scale, the distance on the map is being 2 centimetres, means it is 0.

2 kilometres in real life.

On a 1 to 25,000 and 5 centimetres, it's 1.

25 kilometres.

On a 1 to 50,000 with a distance on the map of 7 centimetres, it is 3.

5 kilometres.

Then we're having a go at measuring curved distances on a map.

What kind of things did you do to make sure that your measurements were as accurate as possible? Your answers might include things like this.

So hopefully you used a piece of paper with a straight edge.

Using anything else would make it quite difficult.

Hopefully you pivoted the paper and you marked off each pivot point.

And really importantly, you ensured that the starting X, it was on the 0 of the scale bar when you read off the distance.

So let's summarise everything we've learned today.

Geographers use cardinal points, intercardinal points, and secondary intercardinal points and bearings to measure direction on a map.

Places and features on an OS map can be located using four and six figure grid references that are made up of eastings and northings.

Geographers use scale ratios and scale bars to tell them the size of features in real life compared to their size on a map.

While there was a lot of content in that lesson for you to be thinking about, really to get to grips with OS maps, it's all about practising those skills.

So if you have access to an OS map, do have a go at practising your grid references, thinking about direction, and checking out scale as well.

There's also online versions if you don't have a paper copy.

Best of luck.