Line Chart, Explained

The line chart is inspired by the marigram. The main difference between the line chart you see here and a marigram is the data: a marigram shows recorded historic data whereas the line chart here shows tidal projections. Marigrams are records of sea level, and so they are much less smooth than the chart you see here.

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.

Making the line chart

One way to visualize this data is with a line chart. We can plot the date and time (T from the table) for the predictions on the x axis, so that the time closest to now is on the left, and we get farther into the future as we move to the right. That looks like this:

We can add a y axis next. On the y axis, we are going to plot the predicted water level (V from the table). That looks like this:

Now we can add each row from our dataset, mapping the T to the corresponding place on the x axis, and the V to the corresponding place on the y axis. We can represent those values as circles for now.

To make this easier to follow, we can connect the dots.

We can clean it up a little bit, removing some pieces that add visual clutter and adding some labels. We can also add a line to represent the bench mark sea level for the station.

And voila! The finished chart. Now you can go back to the live line chart, or see next chart in the series.