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

Today's lesson is all about collecting physical geographical data as part of your fieldwork inquiry.

Let's see what we're going to learn today.

By the end of today's lesson, you'll be able to use a sampling strategy to help you measure the shape and characteristics of a landscape.

There are lots of keywords in this lesson.

Some of them you might know already, but let's go through them.

First of all, sampling.

This is the process of selecting a sample of data to study from a much larger population.

The sample itself is that selection of data.

The sample size is the number of individual pieces of data that are studied in a geographical inquiry.

Bias is where we have an unfair favouritism for or against something.

And a transect is an imaginary line along which samples of data are collected.

There are three parts to this lesson.

Let's look at the first one, how do geographers decide which data to collect? It's not possible for geographers to measure every bit of data that's available to them.

It would be impossible.

It's just not practical to measure, for example, the size of every piece of sediment on a beach or to ask questions to everybody who lives in a town.

We simply don't have the practical means to do that.

Geographers solve this by taking a sample of data.

This is a small selection that can be representative of the total amount of data.

As geographers design their data collection method, they should decide how large a sample size they need.

And a sample size should be large enough for the geographer to be able to form meaningful conclusions.

But it's also got to be small enough that the data collection is manageable within the time and resources that they have available.

So it's a kind of sweet spot in the middle that's needed.

This means the sample size will vary depending on the location, the time available, the nature of the inquiry.

So there's no such thing as the perfect sample size.

The perfect sample size is the one that suits your particular fieldwork inquiry.

So let's check our understanding so far.

Izzy is collecting data on the size of sediment she will find in different courses of a river.

Just remember, that's the upper course, middle course, and lower course.

So three different sites.

She'll have one day to collect the data as well as travel between the sites.

So perhaps not a whole amount of time is available to Izzy.

What would be a sensible sample size for her to use? Let's look at the three options first.

She could collect one piece of sediment in each course.

Maybe 15 pieces of sediment in each course, so that's 45 in total.

Remembering there's three courses that she needs to cover.

Or maybe 100 pieces of sediment in each course.

So that's 300 pieces of sediment that she would have to measure.

Which one do you feel is the most sensible option for Izzy? Well, if you chose B, you would be correct.

I feel that's the most sensible option to Izzy at the moment.

But I would also be having a conversation with her about how long it might take for her to travel between the three different sites.

It could be that she will actually have time to collect a little bit more data, or it could be she'd have to measure fewer bits of sediment if she's really going to be up against it time-wise.

Once geographers have decided on their sample size, they need to decide on a technique they will use to decide which data will form part of their sample and which will be ignored.

This is known as a sampling strategy.

So here we've got Laura.

She's also going to be measuring sediment.

She's saying, "How do I decide which pieces of sediment I will measure?" She's got a quadrat looking like it's on a beach there.

She's trying to decide, well, which bits of the stone there, which ones do I measure, which ones do I ignore? It's quite difficult because there's no way she could measure every single bit of rock that's in that quadrat.

So we've got Sam here.

Now Sam is suggesting that Laura uses a systematic sampling strategy.

This means the geographer uses a predefined system to collect their sample.

So as Sam describes it, she says, "I'm going to measure the size of every 10th rock I find in my quadrat.

There's a system to how I'm selecting the rocks." So every 10th one is the one that she's going to measure.

She's going to ignore all of the others.

Now it could be that Laura might want to choose a random sampling strategy.

This means that the geographer has no control over the data that makes its way into the sample.

And this is a method that Sofia is preferring here.

Sofia says, "I'm going to close my eyes and pick out 15 rocks from inside my quadrat.

By closing my eyes, I'm making the selection a random one." Sofia has no control over which rocks make it into her data and which don't.

Now there's another option for Laura, and that could be a stratified sampling strategy.

This means that the geographer has some kind of preexisting knowledge which they use to create a more representative sample.

Here we've got Jacob and he's advising Laura to do this method.

He says, "I know this area is made up of granite and limestone.

To make my sample representative, I'm going to make sure that 50% of my sample is granite and 50% is limestone." So he has taken some pre-existing knowledge, which is about the geology of the area, and he's using that to inform his sampling strategy.

An important reason for having a clear sampling strategy is to avoid bias.

And this is where the geographer would show favouritism towards some data over others.

Bias has the potential to make conclusions meaningless as the data would not show the whole picture.

And as Sam says there, "All of our sampling strategies avoid bias because we do not know exactly what the data will be like before we start collecting the data." Sampling also involves thinking about where the data collection is going to take place.

For example, on a beach, it's not practical to collect data from the whole area.

You could be looking at a really big space and you may not have time or the means to do so.

So it's important to remember that no sampling strategy is better than any other.

The best choice of sampling strategy is the one that works most effectively with your specific location, time, and most importantly, your inquiry question.

So one way of thinking about sampling spatially is the geographer could sample a series of transects, and they're represented here by the purple lines.

These are imaginary lines between two points along which data is collected.

So the transects here are running from the shoreline closest to the sea, to the back beach, the bits further away from the sea.

Each of those lines would be called a transect.

Not the only way you could do it.

So a geographer could make a sample more random.

They could divide the whole area into a kind of grid, and then some squares are randomly chosen for the data collection.

So you would choose where you would do your data collection based on perhaps a random number generator.

So let's check your understanding.

True or false? Systematic and stratified sampling are better than random sampling.

Is that true or false? Pause the video, have a think about your answer, but also think about why you've chosen that particular answer.

So are some sampling strategies better than others? No.

But why is that? Well, the best strategy to use depends on the location of the data collection, the size of the overall population of data, and what conclusions one hopes to make from the data.

That end one is the most important bit.

What do you actually want the data to do for you? And that's what could decide what sampling strategy you use.

Let's look at our first practise task of this lesson.

Jun wants to collect data about the shape of this beach.

He has decided to collect data from a transect at the eastern end.

And you can see it's marked there on the map.

He has chosen this area because he thinks the beach here has an unusual shape.

What two problems can you identify with Jun's method? Your second task, explain why these are problems. Now this will take some thinking, so do pause the video, read the questions again, and then I'll come back to you with my ideas.

Okay, so let's look first of all at the two problems that there are with Jun's method, and then we'll explain them as well.

The two problems, which I hope you found, is that really Jun's sample size is not large enough.

And secondly, his sampling strategy does tend to show a little bit of bias.

Let's explain those ideas.

So first of all, his sample size is not large enough because he's only chosen one transect across the whole beach.

This means his sample size will not really tell him what the overall shape of the beach is like, only that eastern end where he's put his transect in.

He needs to do a lot more transects really to start being able to conclude in a meaningful way.

The other issue was around bias in his sampling strategy.

So Jun has purposefully chosen the part of the beach that he thinks looks a bit unusual.

It isn't representative of what the whole beach is like, and so his measurements are going to come out in quite a biassed manner.

Let's move on to the second part of today's lesson, which is all about how can geographers measure the shape of the land.

Now, within any landscape, there are various aspects that can be measured.

One might measure, there's some pretty simple dimensions, such as the height of something like some trees, a cliff, how high a sediment buildup might be.

Geographers might measure depth of something like rivers and pools, the depth of an eroded area.

The width of something like a beach, a river channel, a footpath.

There's lots of things which could be measured in that way.

And likewise the length of something, how long sediment pieces are, how long a beach is, how wide and long a woodland area might be.

Then there's another one, gradient, how steep or shallow a river might be, sand dunes and landfalls, how they are angled in relation to a flat plane.

In most cases, these dimensions can be measured just simply using a tape measure or a ruler depending on how large the thing is that you're trying to measure.

But if you are measuring something which is way taller or bigger than your tape measure, then you have to start using other methods.

So measuring the height of a feature such as a cliff or a tree requires a different approach.

Now don't panic about some of the maths that's on the screen at the moment.

Let's go through it step by step.

Initially you need three different measurements to work out the height of a tree or a cliff.

First of all, you need to know how far you are away from the base of that feature.

You then need to think about your own height.

Now, it's not the height to the top of your head, but the height from the ground to your eye level.

The third piece of data you're going to need is the angle between your eye level and the top of the feature.

For this, you're going to be needing a piece of equipment called a clinometer.

It measures the angle between two points.

You can calculate the height of the feature using an equation, which you can see on the screen there, and you will need a calculator to do this.

So using the data that is there on the screen now, the height of the tree is 11.

6 metres.

I would recommend that you pause the video here.

Just check that you can use the calculator effectively with those pieces of data and see that you come out with the same answer, 11.

6 metres.

Let's check our understanding in terms of measuring the shape of the land so far.

Alex is investigating how the shape of a river channel will change from source to mouth.

Which elements of the channel could he measure at his field sites? There's quite a few probably.

Could he measure the width of the channel, the depth, the gradient of a section of a river, the height of the channel above sea level, or the distance of the field site from the source? Bear in mind that Alex is at the river itself when he's trying to measure various things.

Have a think, pause the video, and I'll come back to you.

So what do you think, which elements of the channel could he measure at his field site? Yes, it's those first three.

He could get into the river and measure its width, its depth, and its gradient.

But the height of the river above sea level, he would probably have to use a map for that and wouldn't necessarily be able to do that in the field.

Equally, the distance from the field site would also be a piece of secondary data.

He would have to use another source of information in order to work that out.

Measuring the size and shape of the landscape on its own is unlikely to have a lot of value in a geographical inquiry.

Instead, geographers will compare the size and shape of the landscape and its features with similar places.

For example, one might compare two river channels, one that runs through a granite landscape and one that runs through a clay landscape.

The same dimensions would be measured in both and then they can be directly compared.

Geographers might also look at how the size and shape of landscapes changes over time by comparing their measurements with data that has been collected previously.

The geographers in this photograph are measuring the angle of the beach after a storm to see how the shape has changed, because their hypothesis would be that the heavy rainfall and the strong winds will have shifted the beach sediment around into different places.

Measurements are often paired up to show how each influences the other.

For example, sediment found on a beach with a steep gradient is likely to be larger, while sediment found on a beach with a gentle gradient is likely to be smaller.

So in this case, the geographers are comparing the gradient of the beach with the size of the sediment found there.

Another example.

As the distance from a river source increases, the width and depth of the river channel is also likely to increase.

So in this example, the geographers are comparing three different dimensions: distance from source, width of the channel, and depth of the channel.

Let's do another check here.

So, true or false? Andeep plans on measuring the depth of a river channel.

He will visit one part of the river.

Andeep's data will show how the depth of the river changes from source to mouth.

Will it? Is that true or is that false? Well, I hope you can see here that there is an issue.

It's not going to show him what he thinks it's going to show, but why? Well, Andeep would need to measure river channel depth at a number of sites along the river to compare them.

At the moment he's only visiting one site.

He hasn't got anything to compare it against, so he is not going to be able to say whether the depth of the river changes from source to mouth or not.

Let's do a practise task.

So Lucas is visiting this location to collect data.

You can see we've got a beach location here, we've got a headland, and we've got a shingle beach in front of it.

He wishes to find the size of the various features found here.

And remember, features covers a lot of landscape ideas.

Make a list of the precise measurements that he could record here.

Pause the video.

There's probably more than you think, and I'll come back to you with some of my ideas.

So what are some of the things that Lucas could measure here? Well, he could look at the width of the beach, and we're going to be really precise, he could look at the width of the beach along six equally spaced transects.

They stretch from one end of the beach to the other.

He could look at sediment size, but again, let's be precise.

So we could look at the size of 15 pieces of sediment selected from random areas of the beach.

Lucas could look at the angle of the beach.

He could look at it every five metres along the transects themselves.

He could look at the height of the cliff, again at six randomly sampled points.

He could look at the stack that we saw in the photograph.

He could measure its width.

He could also measure its height, similar to the way that he would measure the cliff height.

Now our final part of the lesson, how can geographers measure land characteristics? So some geographers look in great detail at the characteristics of soil and vegetation cover.

A quadrat can be used to sample vegetation cover.

There's one in the picture below.

One can count and identify different plant species and compare the species diversity of one place with another.

If a grid quadrat is used, and that's what's in the photograph here, and it's called a grid quadrat because you can see it's been subdivided into smaller squares.

If one of those is used, the geographer can count the number of squares that contain vegetation.

From this, they could calculate the percentage of the sample area that has vegetation cover.

So they could basically ratio up those numbers.

Geographers can also look at the soil itself.

An infiltrometer is used to measure how easily different soils or ground surfaces can allow water to infiltrate.

And you can see a picture of an infiltrometer there.

It's the clear tube that has been sunk into the ground.

The infiltrometer is hammered firmly into the ground, and then a set amount of water is poured into the tube.

Geographers record the amount of time it takes for the water to infiltrate.

They can then calculate the infiltration rates for different surfaces, such as sand and gravel and bare soil.

So as you might imagine, the amount of time it would take the water to infiltrate for something like sand would be much less than something like tarmac or a hard bare soil.

Let's check our understanding now.

So Aisha wishes to compare the infiltration rates for two different areas, a wildflower meadow and a football pitch.

Which pieces of equipment will she need? Will she need a quadrat, an infiltrometer, a stopwatch, bottle of water, or a tape measure? And I'll give you a clue here, there's more than one correct answer.

So in order to measure infiltration rates in those two areas, she will need an infiltrometer definitely.

She will need a stopwatch to measure the amount of time it takes for the water to infiltrate into the soil.

And of course, you also need a bottle of water to actually pour into the infiltrometer.

Geographers might also measure the physical quality of an area.

For example, they could investigate air or water pollution.

Particulate air pollution, and that's things like soot and ash in the air, that can be measured using a particle capture card.

There's one in the picture there.

These cards have a sticky surface which airborne particles stick to.

The cards are hung in different areas for a set amount of time, and then they are compared.

So here's an example of a particulate card, and you can see that there's certain ash and bits of dust and things which have stuck to it.

And that's the kind of thing which is in the air, which unfortunately we are breathing in.

The number of squares with significant particle coverage could be counted.

So there's a 10 by 10 grid there, and so you could quite easily convert that into a measure out of 100 for air pollution.

Now, if you're looking at water pollution, geographers use very special paper strips.

You can see again some in the picture there.

The tips of these strips are coated in a substance which changes colour to show the amount of certain chemicals in a water sample.

So chemicals like phosphates and nitrates can be tested for in this way.

The strips are dipped into a sample of pond or river water.

And then the darker the colour of the strip, the more chemical there is present.

So you can see the sample on the left is quite a pink colour, and this shows that there's a high level of nitrates, compared to the sample on the right where there's almost none.

Let's check our understanding.

Complete these sentences with the missing words.

I'm going to pause the video, and you can then have a go at trying to find them.

So let's see what words you manage to fit in here.

Geographers use specialist paper strips to measure water pollution.

These change colour to show the amount of chemicals present.

Geographers also use sticky cards to measure air pollution.

The cards can be hung in different areas where they capture particles.

Hope you got those right.

Let's look at our final practise exercise for today.

Izzy lives in an area where a local farmer sprays nitrate-based fertilisers on the land.

She wants to know if this is having an impact on local plant species diversity and on nitrate levels in the local stream.

Outline the methods Izzy could use to collect suitable data.

You should include information on where she would collect her data, how large her sample size should be, what sampling strategy she should use, and how exactly she's going to collect the data.

Now there's quite a lot to think about here.

She's looking at local plant species diversity as well as the amount of nitrate that there is in the local stream.

Think really carefully about what data she would need and how she is best to go about collecting that data, particularly with the idea of reducing bias.

Pause the video, have a good think, and I'll tell you some of the things which I think Izzy should do in a moment.

Okay, there are lots of things that you could have written about.

Here's some of them.

First of all, Izzy could measure both water nitrate pollution levels and plant species diversity in a transect along the length of the stream in her local area.

So there's lots of ways she could go about measuring these two things in terms of where it takes place.

Transect is one way of doing it.

The stream is already a transect.

It's already a line along which she can measure data.

There could be three sampling sites.

She could measure one upstream of the farmer's land, one next to the farmer's land, and then one downstream of the farmer's land.

So she gets quite a good spread of data around the area where she thinks pollution might be taking place.

This would be known as a stratified sample, and this is because Izzy knows where the farmer's land is.

Remember, stratified sampling means that you have to have some prior knowledge of the area before you select your sample.

So rather than sample the whole area, because she knows where the farmer's land is, she can do a stratified sample.

So she goes upstream, downstream, and in the place where the farmer's land is.

So how would she go about doing it? At each site, Izzy would use a quadrat on the edge of the stream to measure plant species diversity.

She would count the number of plant species that she finds in each quadrat and record this data.

Then she could compare the data in one area with the data in the other two areas, and then she would have an idea of how the species diversity changes from upstream of the farm to downstream of it.

At each site, Izzy would take a small sample of water from the stream and test it using a nitrate strip.

The colour of the strip from one area, which shows the intensity of any nitrate pollution, can then be compared to the colour of the strip from the others.

So she would have three different nitrate strips for the three different samples, upstream, farmer's land, and downstream, and she can compare the colour across all three to find out which one has the most and least nitrate in it.

So we've come to the end of the lesson.

Let's look at what we've learned today.

So geographers use different techniques known as sampling strategies to sample data during fieldwork.

If geographers are measuring the shape of the land, they can look at the height, depth, width, length, and the gradient across different features in the landscape.

Geographers can also measure the characteristics of the land, such as how easily water infiltrates the soil or whether there is pollution there.

Well done.

There was a lot of new information in there, and I hope some of those techniques give you the confidence to go out and collect some physical geography data during your fieldwork.