Heading into summer, many Oregon lakes were well below their average level after consecutive years of drought.
Tony Schick and I wanted to explain how decades of snow pack and rainfall affect drought in The Northwest. And, how some reservoirs used for recreation show little variation and reservoirs used for agriculture can see dramatic swings in levels.
We made the choice to use small multiples to allow the reader to quickly compare which reservoirs have a lot of variation – lines with peaks and troughs in red and blue – and with little variation – the flat gray lines. The dot at the end of the line quickly lets the reader know if this year was above or below average. In this drought year, we see many red dots.
Line charts are a great data visualization choice when you want to show how a value changes over time. But what about when the value is less important than the change itself? Spark lines are a great way to accent the change in the value (up or down, high or low, etc.). Spark lines are common in visualizing daily stock prices where change is more important than the value of the stock, which may be more important on a quarterly basis. My D3.js code is available on GitHub.