Deciles are used to give an element a ranking. For example, a decile rainfall map will show whether the rainfall is above average, average or below average for the time period and area you have already chosen.

How to calculate deciles
If, for example, you had 40 years of annual rainfall records, you would first need to arrange the totals in ascending order (from lowest to highest). Next split them into 10 equal groups, so that in this example there would be 10 groups of four. The first group (four lowest annual rainfalls on record) would be in decile range one, the second group in decile range two, up to the four highest annual totals (highest 10 per cent) being in decile range 10.

If you choose amounts, you will see the quantity of the element requested. For example, choosing the amounts column under Rainfall Maps will show how much rainfall (in millimetres) has fallen for the time period and area chosen.