Choropleth with classification from multiple columns in QGIS?

Question

I want to create a small multiple graph, which is something like this or this.

I know that I can create a choropleth by using the styles panel:

enter image description here

Basically, I pick a column attribute, choose the classification mode, and classify. This results in the legend as pictured above. However, this is bin distribution off of one attribute POP1990, in this case the population in each state in 1990. I have attributes POP1991,POP1992,POP1993, and so on. I can individually classify them, and get 4 different bin distributions. But I want to get the bin distribution off of all POPYEAR columns so that they share one legend (like the small multiple example linked above). Is there a way to do that?

Basically, I want to create 4 individual choropleth maps per year, but I want the legend that they all use to be the same. Is there a way to do this? I know that there is this expression dialog:

enter image description here

But I'm not sure how I would use this to accomplish what I want. I saw this about creating small multiples with virtual layers, but I'm still not sure about the legend.

I'm new to QGIS.

• artwork21: Are you wanting to have many maps in the composer (one for each PoP year) and share one legend?
• ocean800: @artwork21 Yes, thats what I would like! The individual graphs will be based on data per individual year, but I want the color scheme classification to be with all of the year columns if that makes sense.
• artwork21: What do you mean by individual graphs (do you mean maps?)?
• ocean800: @artwork21 Yes sorry maps is the correct word. Something like this
• PolyGeo: As per the Tour there should be no chit chat so please do not include thanks or unnecessary statements of appreciation in your questions.

Answer 1

In simple terms try this:

1. Make duplicate copies (for each year) of layer you want to show in many maps within composer (right click layer in layer panel and select Duplicate option). Rename each layer name to the year which it will represent
2. Style each layer to a different year POP field/column (use common class breaks for each year layer)
3. Create a composer
4. Turn off all layers except for one of the year layers, and zoom to extent if needed
5. In composer, click Add new map button, re-size shift it to where you want it (this should show what is currently turned on in QGIS)
6. Repeat step 4-5 until all year/maps are added within composer
7. Finally, add map title and labels

• ocean800: Thanks! But, I was more confused about generating the common class breaks. The class breaks are generated when a specific POPYEAR is added to create a choropleth. Is there any way in QGIS to create those class breaks from multiple POPYEARs?
• artwork21: Double click on each symbol values range within the style Layer Properties style form and change the value range to whatever common range you want to go with for each layer.
• N00: is there anyway to systematically calculate this common class breaks ?