Graphs & Diagrams (Cambridge International IGCSE Geography)

Spec point — Extract specified geographical information from graphs, diagrams and tables of data

Graphs & Diagrams

Types of data

• Continuous data is numerical data that can take any value within a given range, e.g. heights and weights
• Discrete data is numerical data that can only take certain values, e.g. shoe size
• Quantitative data is where the results can be expressed using numerical values
• Qualitative data is where the results can’t be expressed as numbers, e.g. opinions

Line graph

• One of the simplest ways to display continuous data
• Both axes are numerical and continuous
• Used to show changes over time and space

Example

• A river cross-section is a particular form of line graph because it is not continuous data, but the plots can be joined to show the shape of the river channel

Example of a line graph

Bar chart

• A bar chart is the simplest form of displaying data

• Each bar is the same width but can have varying lengths

• Each bar is drawn an equal distance apart (equidistant)

• The data is discrete data

• Bar graphs are useful for:

  • Comparing classes or groups of data
  • Changes over time

Example

A typical bar graph

Histograms

• Histograms show continuous data
• Always use a ruler to draw the bars
• All bars should be the same width
• The top of the bar should reach the number on the side of the graph that is being represented
• There should be no gaps; all bars should be touching
• Ensure all axes are labelled and that the graph has a title

Example

Example of a histogram

Compound or divided bar chart

• The bars are subdivided to show the information, with all bars totalling 100%
• Divided bar charts show a variety of categories
• They can show percentages and frequencies

Example

Example of a compound bar chart

Population pyramid

• This is a type of histogram
• Used to show the age-sex of a population
• It can be used to show the structure of an area/country
• Patterns are easy to identify

Example

Example of a population pyramid

Pie chart

• Used to show proportions, the area of the circle segment represents the proportion
• A pie chart can also be drawn as a proportional circle
• Pie charts can be located on maps to show variations at different sample sites
• The percentage of the pie chart must add up to 100%
• To calculate degrees of the pie chart (which totals 360°), divide the percentage by 100 and then multiply by 360
• Each segment should be a different colour

Example

Pie chart showing energy sources in an area

Exam Hint To work out the percentage increase/decrease, work out the difference between the two numbers, divide the difference by the first number, then multiply this number by 100.

For example, the difference between 37 and 43 is 6. Then 6 / 37 x 100 = 16.21.

The percentage increase is therefore 16.21%.

Rose diagram

• Uses multidirectional axes to plot data with bars
• Compass points are used for the axis's direction
• Can be used for data such as wind direction, noise or light levels

Example

Example of wind direction being shown on a rose diagram

Triangular graph

• Triangular graphs are used to display data, which can be divided into three

Example

• Read each side carefully so you are aware which direction the data should be considered

  • Always read from 0 to 100 and follow through to the next 0
  • Can be either clockwise or counter-clockwise
  • In the example below, the data reads clockwise

Example of a triangular graph

Scatter graph

• Points should not be connected

• The best fit line can be added to show the relations

• Used to show the relationship between two variables

  • In a river study, they are used to show the relationship between different river characteristics, such as the relationship between the width and depth of the river channel

Example

Example of a scatter graph with a trend line (aka line of best fit)

Types of correlation

• Positive correlation

  • As one variable increases, so too does the other
  • The line of best fit goes from bottom left to top right of the graph

• Negative correlation

  • As one variable increases, the other decreases
  • The line of best fit goes from the top left to the bottom right of the graph

• No correlation

  • Data points will have a scattered distribution
  • There is no relationship between the variables

Examples showing three types of correlation

Worked Example Making predictions from a set of data

• You may be asked to make a prediction for the next step in given data (either table or graph form) in your exam

• Study the data carefully

• Look at the direction in which the data is going

  • Are the numbers increasing or decreasing?
  • Is there a clear pattern forming?
  • E.g. does the data point value change by 3, 4, 6, etc. each time

• Study the scatter graph below, which shows the cost against distance travelled

Cost against distance travelled scatter graph

• Predict what the cost at would be at 1.75 km

• Answer:

  • To predict the cost at 1.75 km, look at the cost at 1.5 km and 2.0 km
  • Then follow the line of best fit to predict the value at 1.75 km
  • Cost would be £1.3

Exam Hint In the exam, you will not be asked to draw an entire graph. However, it is common to be asked to complete an unfinished graph using the data provided. You may also be asked to identify anomalous results or to draw the best-fit line (aka trend line) on a scatter graph.

• Take your time to ensure that you have marked the data on the graph accurately

• Use the same style as the data which has already been put on the graph

  • Bars on a bar graph should be the same width
  • If the dots on a graph are connected by a line, you should do the same

Choropleth map

• These are maps that are shaded according to a pre-arranged key
• Each shade of colour represents a range of values
• It is common for one colour in different shades to be used
• Can be used for a range of data, such as annual precipitation, population density, income levels, etc.

Example

Example of a choropleth map

Proportional symbols map

• The symbols on the map are drawn in proportion to the variable represented
• Usually, a circle or square is used but it could be an image
• Can be used to show a range of data, for example, population, wind farms and electricity they generate, traffic or pedestrian flows

Example

Proportional circles map showing GDP (billion US$) across Europe

Pictograms

• These are a way of displaying data using symbols or diagrams drawn to scale
• Useful way of showing data if accuracy is not too important and data is discrete
• Years do not need to be continuous
• Symbols do not need to be whole but can represent a proportion
• A key is needed to show if the total number of objects or events that image represents exceeds one

How to read a pictogram

• Step 1: Read the problem carefully and identify the specific information requested from the pictogram
• Step 2: Count the symbols corresponding to the desired information and report the count

Example of a pictogram

• In the pictogram above, you can see that 4 shoppers walked to the supermarket, but only one used a taxi
• The majority of shoppers used a car to travel to the supermarket