the line

A line follows one thing over time. Read it left to right and watch which way it leans — that lean is the whole story. A dashed stretch is a guess, not something anyone measured.

What it leaves outThe line implies every point between the dots, and nobody measured those. Where you start and stop it decides what the trend looks like.

1 · basics · cartesian · level 1 · read a chart · taught in dive 2.1 · dive 2.4 · dive 2.5 · dive 3.1 · dive 4.2 · dive 4.3

Two worked examples

Where is this going next?

Before you lookCover the right-hand third of the line. Write down where you think it ends up.

civicprices_us_monthly.csv · 319 rows · 7 columns

what a dozen eggs cost in an average American shop, every month since January 2000

What to look atFollow it left to right, then cover the left half with your hand and look again. Where you start the line decides whether this is a catastrophe, a recovery, or nothing much.

This example draws itself with a small script. With scripting off you can still read every word on this page, and the file itself is at data/prices_us_monthly.csv.

earth and spaceline_co2_mauna_loa_annual.csv · 67 rows · 2 columns

carbon dioxide measured at Mauna Loa, every year since 1959

What to look atNearly straight, and rising the whole way. Sixty-seven readings, each one taken by somebody on a mountain in Hawaii.

This example draws itself with a small script. With scripting off you can still read every word on this page, and the file itself is at data/line_co2_mauna_loa_annual.csv.

the pool

Now build one yourself.

The pool opens with this file and this shape already drawn, so your first move is to change something rather than to start from nothing. Bring your own CSV if you have one. Nothing is uploaded anywhere — the chart is drawn in your browser, your work saves there, and it downloads as a picture or as a project file you can open again.

Open the pool → the line · prices_us_monthly.csv