Ridgeline Chart, Explained
The ridgeline chart is beautiful in its simplicity - it reminds one of the movement of a body of water. Ridgeline charts are a favorite and are often called 'Joy Division' plots due to the album artwork on Joy Division's Unknown Pleasures. To see another ridgeline of mine, check out Bus Joy.
About the data
NOAA makes predicitons for every high tide and low tide for each tide station. The data table has three columns: T, V, and Type. T refers to the predicted time, V to the predicted water level (in feet from bench mark), and Type to the type of tide (high or low). This data comes from NOAA's Tides and Currents Tidal Predictions portal.
| T | V | Type |
|---|---|---|
| 2019-11-08 01:22 | 0.921 | L |
| 2019-11-08 07:53 | 4.668 | H |
| 2019-11-08 14:14 | 1.265 | L |
| 2019-11-08 20:03 | 3.912 | H |
| 2019-11-09 01:54 | 1.132 | L |
| 2019-11-09 08:16 | 4.856 | H |
| 2019-11-09 14:48 | 0.888 | L |
Figure 1: A table showing data from November 8, 2019 and November 9, 2019 showing tidal high/low projections for Moss Landing, Ocean Pier station.
Making the ridgeline chart
Another way to visualize this data is with a layered line chart. This chart was directly inspired by the layered line chart, so it might be helpful to look at how the layered line chart was made before reading this section.
The ridgeline chart shows the predictions for each day stacked, with the prediction closest to now at the top of the chart. So first we have to make an x axis that is 24 hours long:
To make things a little easier to follow, we can add a vertical line at each hour. This will make it easier to compare the ridgelines later on.
Now we can add our first line, showing the predicted water level over the course of one day. We can label this line to make it easier to follow.
Now we can add our second line, showing the predicted water level over the course of the following day, directly below the first day:
We can add all of the days that we have. Now our labels are a bit cramped, and the visual is cluttered.
We can remove some of that clutter so we can see the patterns more easily:
And voila! The finished chart. Now you can go back to the live ridgeline chart, or see next chart in the series.