Radial Chart, Explained
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 radial chart
One way to visualize this data is with a line chart. Because this chart was directly inspired by the line chart, it might be helpful to look at how the line chart was made before reading this section.
The radial chart is very similar to a line chart, but instead of moving from left to right represent date and time (T from the table), we move in a circle. That means the predicted water level (V from the table) will be represented as the distance from the center of the circle. We can add markers to make this more apparent:
The smallest circle is a foot below sea level. The largest circle is six feet above sea level. Now we can add our data, starting from the top of the circle with the data closest to now, and moving clockwise as the predictions get further into the future.
And voila! The finished chart. Now you can go back to the live radial chart, or see next chart in the series.