HANDLING ATTENTION POINTS◆ 179
% ‘Very good’ % ‘Fairly good’
(g) Layer chart
Proportion of UK survey respondents rating the
performance of the railways as ‘very good’ or
‘fairly good’, 2001 (hypothetical)
Use a layer chart whenever:
- you want to show how the relative size of two
positively associated variables varies across time.
Don’t use a layer chart if:
- your two variables are not really linked.
Points to watch:
- put the layers in an order that gives the clearest visible
pattern, e.g. a numerical progression with the largest
layer at the bottom and smaller layers towards the top;
- if the variables have to be kept in a fixed sequence but
this gives a jumbled appearance to the layers, then use
another type of chart.