Their new screencast is awesome too!
"Observable: An Earthquake Globe in Ten Minutes" https://www.youtube.com/watch?v=uEmDwflQ3xE
"Observable: An Earthquake Globe in Ten Minutes" https://www.youtube.com/watch?v=uEmDwflQ3xE
The finished notebook from the screencast (which you can fork): https://beta.observablehq.com/@jashkenas/earthquakes
And a fancier version that spins, reuses the canvas element instead of re-rendering it from scratch, projects the quakes as circles on the surface of the sphere, and offers a bunch of other options to configure (like if you'd like to chart the past day, week or month of quakes): https://beta.observablehq.com/@jashkenas/quakespotter-0-1
You can change which cell is focused using Option-Tab ⌥⇥ and Shift-Option-Tab ⇧⌥⇥. You can also click on the asterisk (*) in the left margin to edit any cell.