Graphs

Key terminology

Key terminology

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 graphs

Line graphs

• One of the simplest ways to display continuous data

• Both axes are numerical and continuous 

• Used to show changes over time or 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

Radial graphs

Radial graphs

• Use multidirectional axes to plot data with bars or lines

Climate graphs

Climate graphs

• A climate graph shows mean monthly temperatures and precipitation rates over 30 years

• They can be local, national, or global  

• Precipitation is always shown as a bar graph and temperature as a line graph

Dispersion graphs

Dispersion graphs

• Dispersion graphs are used to compare sets of data 

• They also illustrate whether the data forms groups or is dispersed (spread)

• Values are shown on the vertical axis

• Can also be used to present the upper and lower values along with the mean, median, mode and extreme values

Doughnut graphs

Doughnut graphs

• Doughnut graphs visually represent proportions as part of a whole

• They are similar to a pie chart but with no centre

Kite graphs

Kite graphs

• Kite diagrams can show both distribution and amounts

  • The distribution along a transect is shown by its position along a line in each section of a kite diagram

    • Each section represents a different species 

    • The distance along the transect is given on the x-axis

  • The numbers are shown by the width of the 'kite' around the central horizontal line

    • The shape is referred to as a kite because it extends an equal distance on each side of the central horizontal line

Triangular graphs

Triangular graphs

• Triangular graphs have axes on three sides, all of which go from 0 to 100

• Used to display data which can be divided into three

• The data must be in percentages 

• Can be used to plot data such as soil content, employment in economic activities

Scatter graphs

Scatter graphs

• 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

• The points on a scatter graph should not be connected

• The best-fit line can be added to show the relationship

Flood hydrographs

Flood hydrographs

• Used to show the impact of a storm event on river discharge

  • The bar chart shows the precipitation total (mm)

  • The line graph shows the river discharge (cumecs)

• The graph shows a short period, usually 24 hours

• The storm hydrograph has several features:

  • Base flow, which is the 'normal' level of river discharge

    • The water mainly comes from groundwater flow

  • Peak rainfall is the highest rainfall level during the storm

    • The time of the peak rainfall is taken from the centre of the bar

  • The rising limb shows the increase in the river discharge

    • The steeper the limb, the faster the river discharge has increased

  • Peak discharge is the highest level of discharge in the river

  • Lag time is the time difference between the peak rainfall and the peak discharge

    • The shorter the lag time, the higher the risk of flooding because the river may not have the capacity to contain the increase in discharge

    • Where there is more overland flow (surface runoff), the lag time will be shorter

  • The recessional limb shows the river discharge returning to normal flow

    • The steeper the recessional limb is, the faster the river returns to normal flow

• The shape of the flood hydrograph indicates some of the factors that may affect the discharge

  • A hydrograph with a steep rising limb and short lag time is likely to be in an area with one or more of the following:

    • Impermeable surfaces (urban areas)

    • Heavy precipitation

    • Snow melt

    • Steep slopes

    • Impermeable soil (saturated or frozen)

  • A hydrograph with a gentle rising limb and long lag time is likely to be in an area with one or more of the following:

    • Rural area with trees

    • Permeable surfaces

    • Gentle slopes