Lab 2.5 – Bubble charts

Fundamental concept: Variability in the data, finding trends
Estimated time to complete: 15 minutes
Materials needed (none)

How can several variables be presented on a map?

Sometimes maps are very useful when presenting data because the data are strongly tied to the geography. It is easy to plot locations on a map, you just need to know the latitude and longitude of the point you wish to plot. But how can you plot data associated with that location point? For example, the depth of earthquakes can tell us the depth to a subducting tectonic plate, so attaching earthquake depth data to earthquake location data is important to marine geologists. You could plot the location of each earthquake on a map and attach text (the depth) to each data point, but it is difficult for people to read and process a lot of text, especially numbers.

  1. Can you think of a way to modify the dots used to plot earthquake locations so they also contain information about the depth of the earthquake? Once you have pondered this click the button below to see how geologists do this very thing.

The dots are now color-coded to show the depth of the earthquake (measured in kilometers below the Earth’s surface). By comparing to the color bar in the upper left, we can tell which earthquakes occurred close to the surface (white and pink) and which were deep below the surface (blue).


In the figure above, the depth of the ocean is indicated by shades of blue (darker blue indicates deeper water). The dark blue groove that runs from the northeast to the southwest of this map is a deep seafloor trench.

  1. What is the depth of the earthquakes that are closest to the trench?
  2. What is the depth of the earthquakes that are farthest from the trench?