Arguably the most used type of graph, this line graph demonstrates that GD::Graph,
even using 'default' settings, can produce a comprehensive graph with legible output
Colours of the graph line data sets are 'picked' by GD::Graph automatically.
Whilst these can be manipulated directly, when a lot of data sets are plotted together
with a legend, controlling the correct sequencing of appropriated colours can become a bit of a headache.
Letting GD::Graph just 'get on with it' as far as colour allocation of data sets takes a lot of head work out of the job.