Since #3013, it is possible to plot multiple metrics using the ImageGraph API.
This feature is available but not used in scheduled reports. Scheduled reports rely on the metadata 'imageGraphUrl' field.
The metadata 'imageGraphUrl' field does not currently specify any metric to plot.
In absence of a specified metric, the ImageGraph API plots 'nb_visits' by default.
If 'nb_visits' is not available for a specific report, the first metric found in the metadata 'metrics' field is used.
As an example, the Actions - Main metrics report (actions-main-metrics.png) plots the 'pageviews' metric.
While this is a fine default metric, it would be even more useful to additionally plot 'downloads' and 'outlinks'.
Other reports would also benefit from plotting conversion rates see #3793.
This ticket is about finding a way to define which metric(s) should be plotted by default in graphs.
An immediate natural way to proceed would be to add yet an additional metadata entry.
Attachment: Actions - Main metrics
Proposal: new entry in metadata: "defaultMetrics" that would be set only for the reports which have special rules (eg. Actions.get method defaultMetrics:["actions","downloads","outlinks"] )
Then the static graph builder would look for this metadata and if set, plot the specified metrics.
Piwik Mobile will automatically benefit from the default good looking graphs as well.