discharge m³/s rainfall mm 1 aqa geo4b geographical issue evaluation skills photocopiable/digital...
TRANSCRIPT
1
Dis
char
ge m
³/s
Rain
fall
mm
AQA GEO4BGeographical Issue Evaluation
SkillsPhotocopiable/digital resources may only be copied by the purchasing institution on a single site and for their own use
© ZigZag Education, 2013
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Geographical Investigation
Graphical Techniques
Hydrograph
Bar Chart
Line Graph
Simple
Comparative
Compound
Divergent
Pie Chart
Radar Graph
Climate Graph
Proportional circles
Kite & radial diagrams
Scattergraphs
Triangular graphs
Logarithmic scales
Basic SkillsAnnotation
Photos
OS maps
Base maps
Graphs
Diagrams
Sketch maps
Use of overlays
Literacy skills
Investigative Skills
Identify geographical questions
Data selection & collection
Sampling methods
Random
Stratified
SystematicQualitativeQuantitativePrimarySecondary
Processing data Interpreting data
Risk assessment
Drawing conclusions & assessing validity
Evaluation
Evaluate geographical information
Evaluate geographical issues
Statistical Techniques
Spearmann Rank
DisparityInterquartile range
Standard deviation
Mean, Median, Mode
Comparative testsChi Squared
Mann Whitney U test
Cartographical Skills
GIS
Choropleth
OS maps1:25,000
1:50,000
Isoline maps
Dot maps
Base maps
Sketch maps
Town centre plans
Proportional symbol maps
Flowline
Desire line
Trip lines
Synoptic charts
Use of ICT
Remotely sensed data
Digital images
Photos
Satellite images
Data Presentation
GIS
Statistics
Use of databases
Census
Environment Agency
Met Office
You can be asked to undertake any one of the skills shown on the previous slide.
However, some are going to be more appropriate to the pre-release material than others.
Do make sure that you are familiar with all of the different calculation methods and that you take a calculator and full maths set (protractor, compass, ruler) into the exam.
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WHAT SKILLS DO I NEED?
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STREAM ORDER HIERARCHYThis is a simple method of classifying the size of a stream based on the number of tributaries it has of certain sizes.
When two tributaries of the same size meet, the stream moves up the hierarchy, e.g. when two first-order streams meet, they create a second-order stream.
However, if a first-order and a second-order stream meet they simply remain a second-order stream. It needs the meeting of two second-order streams to create a third-order stream.
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SIX-FIGURE GRID REFERENCES
Top Tips: Read ‘along the corridor and up the stairs’ to get the four-figure grid
reference. Use a ruler to measure exactly how far across the square you need
to go (you need to subdivide each square into 10 segments). On a 1:25,000 map, 4 mm is 1 segment across. These form your
third and sixth numbers of the six-figure grid reference. Don’t forget, if what you are looking for is on the line then the third
(if going along) or sixth (if going up) number is 0.
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DRAWING A CROSS-SECTION
1. Identify the cross-section on your OS map (if possible, draw a faint pencil line so you don’t lose your place).
2. Look at how the contour lines change across your profile; follow them round until you find out their height.
3. What would you expect the land to be doing either side of the river?
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4 O
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Surv
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0402
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7
60
50
40
30
20
10
00 50 100 150 200 250 300 350 400 450 500
1. Use the scale on the OS map to help you understand the distance you will be travelling – 4 cm = 1 km, therefore 2 cm (the distance of the transect given in the question) = 500 m. 4 mm = 50 m.
2. Plot your axis labels on your graph – along the horizontal axis needs to be your distance (0–500 m going up in 50 m intervals). Along the vertical axis needs to be the height of the land – check your transect – what’s the highest point shown?
3. Now make your first plot (0 m – the start of the transect should be 60 m high.)4. Now measure 4 mm (50 m from the start of the transect). What is the height of the land?
Plot this in the correct place on your graph.
DRAWING A CROSS-SECTION
x
x
60m
6. Now continue working your way along the transect line and plotting the heights.
7. Finally, join the crosses up with a smooth curve.
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COMPLETED CROSS-SECTION
River
Distance in metres across the cross section
Hei
ght o
f lan
d (m
)
PLOTTING A FLOOD HYDROGRAPH
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How to plot it:1. Choose a suitable scale for the
axes – you can have one scale for rainfall and another for discharge.
2. Plot the rainfall as bars first.3. Plot the discharge as a line.4. Identify the peak rainfall
(highest amount).5. Identify the peak discharge
(highest amount).6. Calculate the lag time (time
between peak rainfall and discharge).
7. Is the rising limb gentle or steep?
8. Is the falling limb gentle or steep?
9. What is unusual about the Wansbeck hydrograph? Can you suggest why?
10 20 30 40 50 60 70 80
Hours from start of storm
1
2
3
4
5
6
7
8
Rai
nfal
l (m
m)
0
50
100
150
200
250
300
350
400
0
Dis
char
ge (
m³/
s)
Rainfall River flow
Peak Rainfall
Peak Discharge
Secondary discharge peak
1st Peak Rainfall
Lag time = 3 hours
Stee
p ris
ing
limb
Steep falling limb
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This graph shows the distribution of data around the mean or median.
It is plotted as a line with a series of dots recorded if there are several pieces of data that are the same.
The points are NOT joined up.
HOW TO PLOT A DISPERSION GRAPH
Rainfall data for 5th–7th September
Note how the number of hours when there was no rainfall recorded really skews the mean and median data.
Mean
Median
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1. The mean is very straightforward; this is the average – add up all the data and then divide by the number of pieces of data you have.
2. For the median, you need to put all your data in order. Then find the middle number – this is the median. If you have an odd number of data sets this is easy, e.g. I have 51 sets of data so the median number will be the data found at number 26 as I count up. If you have an even number of data sets, you will need to split the difference between the two middle numbers, so if you have 50 sets of data you need to add the data you find at 25 to the data you find at 26 and then divide it by 2 to get your answer.
3. The mode is the most frequent number, so if in a list of numbers ‘15’ occurs five times and the other numbers only occur once or twice, then 15 is the mode.
CALCULATING THE MEAN, MEDIAN AND MODE
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This is a method used to show the spread (dispersion) of a set of data around the median. It is calculated by finding the difference between the upper and lower quartiles, which shows where 50% of all data is found.
The smaller the interquartile range, the more the data is grouped around the median showing that there is not much variation between the data.
INTERQUARTILE RANGE
Using the formulae provided, state the upper quartile (UQ), lower quartile (LQ) and the interquartile range (IQR) for your completed dispersion diagram.
UQ = th position in the rank order =
LQ = th position in the rank order =
IQR = UQ – LQ =
n = number in the sample3.2 mm
0.0 mm
3.2 – 0.0 = 3.2 mm What does this tell us about the spread of rainfall over these three days?
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1. Standard deviation is used to show the amount of clustering of each individual value around the mean. Its symbol is σ (the Greek letter sigma).
2. A low standard deviation shows that the data is clustered around the mean value, whereas a high standard deviation shows that the data is widely spread with some figures being significantly lower or higher than the mean.
3. The formula is easy: it is the square root of the variance. The variance is the average of the squared differences from the mean.
4. To calculate the variance: Work out the mean () (the total of all the data divided by the number of pieces of
data = n). Then subtract the mean from each number and square the result (the squared
difference). Then work out the average of the squared differences. Now you can calculate the standard deviation by square-rooting the variance. Then you need to decide whether your data is clustered or not.
STANDARD DEVIATION
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Time River flow (cumecs)
00.00 57 01.00 67.3 02.00 78.5 03.00 85.7 04.00 93 05.00 99.2 06.00 107 07.00 124 08.00 145 09.00 169 10.00 191 11.00 217 12.00 243 13.00 269 14.00 297 15.00 337 16.00 357 17.00 324 18.00 304 19.00 275 20.00 241 21.00 215 22.00 206 23.00 213
-139.57-129.27-118.07-110.87-103.57-97.37-89.57-72.57-51.57-27.57-5.5720.4346.4372.43100.43140.43160.43127.43107.4378.4344.4318.439.4316.43
19479.78
16710.73
13940.52
12292.16
10726.74
9480.92
8022.79
5266.41
2659.47
760.10
31.02
417.38
2155.75
5246.11
10086.18
19720.58
25737.78
16238.4
11541.2
6151.27
1974.03
339.66
88.92
269.94
4714.7 = 196.57 199337.84
= Standard deviationX = Individual value = Meann = Number in the sample = Sum of
𝜎=√∑ ( 𝑋− 𝑥 )2
𝑛
= √8305.74 = 91.14
This standard deviation result shows a wide spread around the mean showing considerable fluctuation in discharge during the day.
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Scatter graphs can be used to show the relationship between two data sets. However, it is only a ‘best fit’ relationship. For accuracy, Spearman Rank Correlation Coefficient can be used to prove the strength of a relationship.
Once points are plotted, a line of ‘best fit’ can be drawn. The pattern of the scatter graph shows the relationship between the data. With a positive relationship, as one set of data increases, so does the other. With a negative relationship, an increase in one data set causes a decrease in the other.
SCATTER GRAPH
0 5 10 15 20 25 30 35 40 4505
1015202530354045
0 5 10 15 20 25 30 35 40 450
5
10
15
20
25
30
35
40
45Positive Relationship Negative Relationship
Line of Best Fit
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Cumulative frequency is when the data of one section is added to the data of the next section to give a running total.
This is particularly useful for giving an idea of how rainfall builds up over time and for showing why the ground would eventually become saturated leading to overland flow.
When plotted, cumulative frequency leads to a curve on a graph.
WHAT DO WE MEAN BY CUMULATIVE FREQUENCY?
0 5 10 15 20 25 30 350
10
20
30
40
50
Figure 2 – 5th September
Cumulative rainfall (mm)
Dis
char
ge (c
umec
s)