Data Dive · Rung 1 · What's There · 1.4

The icon is a unit, and it breaks

Two ways a picture graph falls apart -- at the top of one file and the bottom of another.

Runs in 25 minutes · everything you need is on this page · no network, no accounts, nothing for the students to open

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The trees

Los Angeles street tree inventory

Los Angeles street tree inventory, largest entries810,931 recorded planting sites - data.lacity.orgplanting sitesrecorded entrya tree speciesan EMPTY site - not a tree58,360116,7200Vacant - Ok To Crape MyrtleMexican Fan PalAmerican SweetgSouthern MagnolIndian Laurel FJacarandaLondon PlaneCamphor TreeCanary Island P

Top entries, 810,931 recorded planting sites

116,720
the largest entry
45,000
the largest actual species

Does it belong on a chart of trees by species? There is a real answer on both sides. Let them argue it.

Read the top bar out loudVACANT -- OK TO PLANT. That is not a tree. It is an empty place where one could go, and it is two and a half times the biggest species that is a tree.
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The planets

Exoplanets by how we found them

Confirmed exoplanets by how we found themNASA Exoplanet Archive - transit has found 4,688, disk kinematics oneplanets founddiscovery methodconfirmed planets2,3444,68804,688Transit1,200Radial Velocit283Microlensing98Imaging42Transit Timing17Eclipse Timing9Orbital Bright8Pulsar Timing6Astrometry2Pulsation Timi1Disk Kinematic

5,981 confirmed planets, NASA Exoplanet Archive

4,688
found by transit
1
found by disk kinematics
7 of 11
methods that vanish

Pick an icon: one dot = 100 planets. Now draw it. Seven of the eleven methods round to zero and leave the chart entirely.

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The point

The encoding made an absence

Those seven methods found real planets. The chart says they found none. Nobody lied; somebody chose an icon size.

The three questions
  1. One icon stands for how many? Who decided that?
  2. Which categories disappear at your icon size?
  3. Walk your street. Which of these species is on it -- and is there a gap where a tree should be?
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After the dive

The shapes on this page, in the library’s own words

the picture graph

One little picture per thing, lined up so you can count them.

What it leaves outCounting stops working somewhere above a couple of dozen, and a row too long for the page gets cut rather than shrunk.
the bar

Bar length is the value, so it only means anything measured from zero. Start the axis anywhere else and the lengths stop matching the numbers.

What it leaves outOrder is a choice. Sorted by size it is a ranking; sorted by name it is a lookup; and the same bars say different things in each.

library · ladder · dives · the pool · this dive’s worksheet

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