Swans and Geese
Ellesmere (Te Waihora) is a huge shallow lake south of Christchurch, which partially connects with the sea—in fact they bulldoze a channel to the ocean when they want to lower the lake level. As part of a conference on the management of te Waihora, I designed a poster for Ken Hughey of Lincoln University.
One of the things Ken wanted to depict was the population fluctuations of Canada geese (Branta canadensis) and black swans (Cygnus atratus) on the lake. He had several years of historical data, though fewer for swans than geese, and wanted to show how goose numbers had dropped below their optimum population level.This is the goose graph; the swan one looked much the same but with fewer bars.
The first thing I decided to do was place both sets of data on the same axes. Because the population data were continuous, it made more sense to link them in a line graph, which I created in Ken’s Excel file and copied into Illustrator. Normally I spend five minutes with the direct selection tool deleting all the crap that Excel adds to its graphs; in this case it was simpler to select the trend lines alone and pull them into a new layer, the create axes and numbers from scratch, using the original graph in the background layer as a guide.
(By the way, not many people seem to know that you can drag whatever’s selected from one layer to another by dragging that little colored square 
near the layer’s name.)
To color the goose trend line, I used the eyedropper to sample some brown from a photo of a Canada goose; I just made the swan line black. Those colors were applied directly to the text in the title, as I didn’t want to have a key or legend. Working from Googled photos of each bird, I created silhouettes to label each line, again to avoid a key. It was easy enough to annotate the graph with a level line.
When a graph isn’t working, our temptation is to jazz it up. Excel has any number of ways of making graphs fancier: WordArt, shadows, gradients, 3D, backgrounds and so forth. But this usually makes things worse. Ken had used some of these in his lake level graph, but I thought it needed some simplifying.
I used the same color palette, stroke thicknesses, and font as in the swan and goose graph, so they looked like they belonged together on the poster. It was important, I felt, to translate the rather cryptic numbering scheme for lake openings into English, and to annotate the graph with lines to show the duration of lake openings, rather than just listing dates.
If I were to do this again from scratch, I might use a series of little horizontal lines, one at each sampling time, to represent the lake level, rather than a continuous line.
There’s more information on Ken Hughey’s Waihora research at his group’s web site. Thanks to Ken and to EOS Ecology, for whom I did the design work, for permission to reproduce these graphics. I especially appreciate it when a scientist is brave and altruistic enough to let me post their “before” versions in a forum like this.
My posting frequency has taken a hit since I started working full-time as an information designer, but when the ukulele book is finished I’ll be posting more regularly to Numberpix. The project for 2008 is to finish Pictures of Numbers, my book on data presentation. If readers of this blog have any suggestions for content, you’re welcome to email me: I’m mike, at numberpix.com.
