Representing Agricultural Survey Items in an Atlas:

• Standard deviation has been chosen as the best method to display the data because:
  • The maps are a representation of the survey data showing distribution density.
  • Continuity is maintained as the same methodology has been applied to each category and year.
• Graduations of colour from light to dark on the maps indicate the increase in distribution density of each category across England.
  

Standard Deviation:

• Standard deviation shows the extent to which a value differs from the mean of all the values.
• When data is classified using the standard deviation method, all the data is placed in a 'class' above or below the mean.
  • Each class is either 0.5, 1, 2 or > 3 'standard deviations' from the mean.
  • The data can then be assigned to the appropriate class and coloured on the map accordingly.
  • Once the mean (average) is calculated, the standard deviation can be calculated and the classes defined.