Graphics Programs Reference
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instead scored in the 89 th percentile, which according to the statistical model,
was not progress. Most would agree that students wouldn't earn the scores
they did with a poor teacher. The challenge is that there's uncertainty and
variability within teacher ratings. A rating represents a distribution of teachers,
who are ranked based on estimates with uncertainty attached, but the ratings
are treated as absolute. A general audience won't understand that concept,
so it's your responsibility to and communicate it clearly.
When you don't consider what your data truly represents, it's easy to accidently
misinterpret. Always take uncertainty and variability into account. This is also
when context comes into play.
CONTEXT
Look up at the night sky, and the stars look like dots on a flat surface. The lack
of visual depth makes the translation from sky to paper fairly straightforward,
which makes it easier to imagine constellations. Just connect the dots. However,
although you perceive stars to be the same distance away from you, they are
actually varying light years away.
If you could fly out beyond the stars, what would the constellations look like?
This is what Santiago Ortiz wondered as he visualized stars from a different
perspective, as shown in Figure 1-25.
The initial view places the stars in a global layout, the way you see them. You
look at Earth beyond the stars, but as if they were an equal distance away
from the planet.
Zoom in, and you can see constellations how you would from the ground,
bundled in a sleeping bag in the mountains, staring up at a clear sky.
The perceived view is fun to see, but flip the switch to show actual dis-
tance, and it gets interesting. Stars transition, and the easy-to-distinguish
constellations are practically unrecognizable. The data looks different from
this new angle.
This is what context can do. It can completely change your perspective on a
dataset, and it can help you decide what the numbers represent and how to
interpret them. After you do know what the data is about, your understanding
helps you find the fascinating bits, which leads to worthwhile visualization.
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