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---
## Acknowledgements
## Acknowledgements & References
Thanks to Alex Hale, Andrew McNutt, and Jessica Hullman for sharing their materials.

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## Today
- Grammar of Graphics
- Types of Data
- Intro to Altair
- What is a **grammar of graphics** and how do we use it in practice?
- What **types of data** do we encounter, and how does that affect visualizations?
- Introduction to **Altair**
---

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---
theme: custom-theme
---
# Perception & Color
## CAPP 30239
---
## Today
- What matters most when creating a visualization?
- How does human **perception** factor into visualization design?
- Understanding **color**, and computational representations of it.
---
## What is the most important question when creating a visualization?
---
## What is the most important question when creating a visualization?
<ul>
<li><s>Where will the data come from?</s>
<li><s>What type of chart do I use?</s></li>
<li>Who is the audience?</li>
</ul>
---
## Audience First
- Who are you presenting to?
- How familiar are they with the data?
- What is their numerical & visualization literacy?
- Via what medium will they receive the information?
- What are you trying to do? (Persuade, Inform, Inspire?)
*Only now can we start thinking about data and presentation.*
---
## Perception
- **Selective** - We can only pay attention to so much.
- **Patterns** - Our brains are pattern-matching machines, audience will benefit from intentional patterns & be distracted by unintentional ones.
- **Limited working memory** - We hold a very limited set of information in our minds at once.
---
## What do you see?
<div class="container">
<div class="col">
![](example1a.png)
</div><div class="col">
```python
alt.Chart(random_df).mark_point().encode(
alt.X("a"),
alt.Y("c"),
alt.Color("b"),
alt.Size("c"),
alt.Shape("a:N"),
alt.Fill("b"),
alt.Opacity("b"),
)
```
</div>
</div>
---
## What do you see?
<div class="container">
<div class="col">
![](example1b.png)
```
alt.Chart(random_df).mark_line().encode(
x="a",
y="c",
)`
```
</div>
</div>
---
## Effectiveness Revisited
![width:800px](effectiveness.png)
---
<div class="container">
<div class="col">
**Altair Channels**
- Position (`X, Y`)
- Angle (`Angle`)
- Area (`Radius`, `Size`)
- Hue, Saturation (`Color`)
- Texture (`Opacity`, `Fill`)
- Shape (mark type, `Shape`)
</div>
<div class="col">
**What about?**
- Length
- Slope
- Volume
- Density
- Connection
- Containment
</div>
</div>
---
**Derived Properties**
- Length/Area - size of bars (`X`, `Y`)
- Slope & Density - affected by scale
- Connection - ex. layering of lines w/ points
- Containment - achieved with layering
What about *volume*?
---
## Stevens' Power Law
Stevens (1975): Human response to sensory stimulus is characterized by a power law with different exponents with different stimuli.
perception = (magnitude of sensation)<sup>a</sup>
Smaller <sup>a</sup> exponent: harder to perceive changes.
Stevens measured values of a by exposing people to varied stimulus and asking them to compare magnitudes.
---
<div class="container"><div class="col">
![](stevens.png)
</div><div class="col">
| Continuum | Exponent |
|-|-|
| Color Brightness| 0.33-0.5 |
| Smell| 0.6 |
| Loudness | 0.67 |
| **Depth Perception** | 0.67 |
| Area | 0.7 |
| 2D Planar Position | 1.0 |
| Warmth | 1.3-1.6 |
| Color Saturation | 1.7 |
| Electric Shock | 3.5 |
</div></div>
---
## 3D Graphs
![](stunning-3d-chart.jpg)
---
![](datavizproject.png)
---
![](3d-scatter.png)
---
## Instead of 3D Graphs
- Find other channels: hue & size are good candidates.
- Combine different dimensions into side-by-side 2D graphs.
TODO: example of 2D decomposition of a graph
---
## Color
---
## Acknowledgements & References
Thanks to Alex Hale, Andrew McNutt, and Jessica Hullman for sharing their materials.
- https://www.math.csi.cuny.edu/~mvj/GC-DataViz-S23/lectures/L6.html
- https://en.wikipedia.org/wiki/Stevens%27s_power_law

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/* custom-theme.css */
/* @theme custom-theme */
@import "default";
.container {
display: flex;
}
.col {
flex: 1;
}