QGIS » QGIS Application

This is originally inspired by this request (in french, but full of screenshots): http://www.forumsig.org/showthread.php/43135-Histogramme-cat%C3%A9goris%C3%A9

Trying to summarize: the aim is to create a histogram that could help to compare evolution of both quantity and quality. Let's take the example of analysis of nitrate production for years (2012-2015).

gid	site	year2012	year2013	year2014	year2015
1	foo	6	12	22	22
2	bar	11	5	8	10
3	baz	5	17	21	16

Also according to the quantity, there's a classification of the site quality :

• quantity<=10 --> Good quality
• 10<quantity<=16 --> Bad quality
• quantity>16 --> Very bad quality

Currently, I can display a histogram showing for each site the quantity of nitrates reported each year.
This feature request is to be able to also display the quality (eg. green, yellow, red), so that the histogram would easily present to any reader the evolution of the quality of the site at the same time.

As you could see in the linked discussion, there's a workaround using symbols placement and offset but not user-friendly at all.
An idea of implementation could be to allow expression-based color for assigned attributes.