Visualising city energy policies

I've just finished an interesting project on urban sustainability, showing how different greenhouse gas reduction policies in cities around Europe and China could affect health and wellbeing. I was working for the URGENCHE project (Urban Reduction of Greenhouse Gas Emissions in China and Europe), funded by the EU under FP7. As part of the project, I wanted to draw some Sankey diagrams to show the different energy flows in the cities.

The academics in Stuttgart had already drawn a very detailed Sankey diagram using eSankey! Which was a great starting point for me.

Also, of course, all the technical data collection had been done, and they provided me with all the raw numbers in Excel format.

I wanted to make the diagram a bit clearer though. It needed to be quicker to understand so that policy-makers in the city could see at a glance what the different scenarios and cities would be like. Also, the text needed to be legible on a powepoint slide or an A4 report page.

Looking around for inspiration, I came across this diagram that seemed to be trying to do something similar to what I wanted - looking at different alternatives in an approachable way that was easy to understand.

However, for visual style, I was interested in some of the work by Density Design, particularly the following infographic poster by Stefano Lari:

The poster is rather beautiful, but perhaps over-complex, for my needs at least. Initially, I wanted to try and use the same isometric (pseudo-3D) perspective as the main image on Lari's poster. It's a technique I've had some success with in the past, and I thought it might help to situate the viewer within the context of the city. My initial sketchings led to this, which I presented to project stakeholders in Kuopio, Finland:

I wanted to connect the energy sources to the different sectors (residential, commercial, industrial, transport) and also to show what kinds of things the energy would finally be used for (lighting, heating, etc) using stacked bar charts under the different sectors.

I didn't get a lot of feedback from the meeting, but went ahead and started developing my ideas a bit further in Illustrator.

Initial attempts at the isometric perspective ran into depth problems with the flow arrows. In a normal Sankey diagram, flows can cross quite easily, but not so with the 3D arrows. I had the top layers crossing, and had to do what I could with the sides:

It kind of works, but isn't elegant.

I then immediately ran into issues with the stacked bars:

I didn't like the way they messed with the perspective - the "floor" of the graphic was quite clear before, but now there was a disconnect between the bottom level of the energy generation and the usage sections.

Hanging bars were better, but not easy to label:

Also, I wasn't happy with the diagonal baseline for the bar charts - this can make it hard to compare the relative height of the bars properly, and would have needed some serious justification.

At this point, I decided to rearrange the resources a bit to make the flows overlap a bit less - although I still wanted the bottom-left edge of the four sector boxes free for the hanging bar chart:

 It looked neater with the sources arranged in a semi-circle:

I worked this up in illustrator, but struggled to label the resources properly.

I used flat arrows for the flows in the end as this seemed easier than the slightly clunky crossing over 3D arrows.

I still wasn't quite happy with the layout, but another project meeting was coming up (Rotterdam this time) so I threw in some real data and got ready to present:

This time I got a lot more feedback (amazing how showing something more developed focusses the mind...) There were a lot of questions about the sources of the energy - what was imported, what was generated inside the city... Also, District heat is in some ways rather different to the others, which are more like imported resources. Also, it was agreed that rather than looking at the end uses (lighting, heating, etc) it was more appropriate to focus on CO2 emissions or health impacts (the focus of the project) and the difference between cities.

I went back to the drawing board at this point. It seemed that what was needed was a rethink about what the graphic was showing. I came up with the following adaptation to show energy sources and CO2 emissions with pie charts:

However, this bothered me. 3D pie charts often incur the wrath of information graphic designers everywhere, since it is more difficult to compare the angles involved after the transformation that leads to the illusion of depth. Perhaps I could use "stacks" instead for the carbon, and include other arrows to show the sources of electricity and heat?

However, I was still bothered about the use of Sankey diagrams in isometric perspectives. Stefano Lari gets away with it in his diagram because the flows are either going diagonally down and right or down and left, so the distortion is not an issue. In mine, however, they were going in several different directions. I decided that the perspective was probably holding me back more than anything, and decided to try redrawing in plain old 2D:

As noted in my scrawled note at the bottom, I still hadn't solved the problem of what energy was generated within and without the city. A few hours hard thought and careful trawling through the data, and I had a breakthrough. What if I combined all the different energy generation methods in the city into one node, called "local power plants"? Then I could show how much electricity and heat was generated in the city, and also include things like waste that were produced by the city and used for energy...

A quick rearrangement, and everything was starting to fall into place:

From here, it was just a matter of getting all the data into the new layout in Illustrator:

I decided that, since the circle at the bottom was supposed to represent the city, it would be good to use the outline of the city in question:

One last change, I decided to go back to the the way I had been doing the arrows initially, with the flows coming parallel to each other out of the sources and branching later on - also running parallel into the sector boxes at the bottom:

We eventually used this layout for other cities, and also different scenarios. Here is the one for Basel, based on 2010 data:

In the end, we couldn't get access to the data on CO2 emissions, but I think the diagram is a useful way of showing the quantity of different kinds of energy used by different cities. Possibly the most useful thing about the diagram is for powerpoint presentations. I found that we could switch between the different scenarios for the same city at different time points, and with different policies in place, and see how the energy flows changed.

Overall I'm quite pleased with the diagrams. They may not be the most innovative data visualisations, but sometimes there's a lot to be said for just executing a standard technique like a Sankey diagram with decent labelling...