Aesthetic mappings

class: center, middle, title-slide

.title[
# Aesthetic mappings
]
.author[
### Claus O. Wilke
]
.date[
### last updated: 2024-01-29
]

---

class: center middle

## Plots map data onto graphical elements

---

## Dataset:<br>Daily average temperatures for various locations

.small-font[.center[
<table>
 <thead>
  <tr>
   <th style="text-align:left;"> location </th>
   <th style="text-align:right;"> day_of_year </th>
   <th style="text-align:left;"> month </th>
   <th style="text-align:right;"> temperature </th>
  </tr>
 </thead>
<tbody>
  <tr>
   <td style="text-align:left;"> Death Valley </td>
   <td style="text-align:right;"> 1 </td>
   <td style="text-align:left;"> 01 </td>
   <td style="text-align:right;"> 51.0 </td>
  </tr>
  <tr>
   <td style="text-align:left;"> Death Valley </td>
   <td style="text-align:right;"> 2 </td>
   <td style="text-align:left;"> 01 </td>
   <td style="text-align:right;"> 51.2 </td>
  </tr>
  <tr>
   <td style="text-align:left;"> Death Valley </td>
   <td style="text-align:right;"> 3 </td>
   <td style="text-align:left;"> 01 </td>
   <td style="text-align:right;"> 51.3 </td>
  </tr>
  <tr>
   <td style="text-align:left;"> Death Valley </td>
   <td style="text-align:right;"> 4 </td>
   <td style="text-align:left;"> 01 </td>
   <td style="text-align:right;"> 51.4 </td>
  </tr>
  <tr>
   <td style="text-align:left;"> Death Valley </td>
   <td style="text-align:right;"> 5 </td>
   <td style="text-align:left;"> 01 </td>
   <td style="text-align:right;"> 51.6 </td>
  </tr>
  <tr>
   <td style="text-align:left;"> Death Valley </td>
   <td style="text-align:right;"> 6 </td>
   <td style="text-align:left;"> 01 </td>
   <td style="text-align:right;"> 51.7 </td>
  </tr>
  <tr>
   <td style="text-align:left;"> Death Valley </td>
   <td style="text-align:right;"> 7 </td>
   <td style="text-align:left;"> 01 </td>
   <td style="text-align:right;"> 51.9 </td>
  </tr>
  <tr>
   <td style="text-align:left;"> Death Valley </td>
   <td style="text-align:right;"> 8 </td>
   <td style="text-align:left;"> 01 </td>
   <td style="text-align:right;"> 52.0 </td>
  </tr>
  <tr>
   <td style="text-align:left;"> Death Valley </td>
   <td style="text-align:right;"> 9 </td>
   <td style="text-align:left;"> 01 </td>
   <td style="text-align:right;"> 52.2 </td>
  </tr>
  <tr>
   <td style="text-align:left;"> Death Valley </td>
   <td style="text-align:right;"> 10 </td>
   <td style="text-align:left;"> 01 </td>
   <td style="text-align:right;"> 52.3 </td>
  </tr>
  <tr>
   <td style="text-align:left;"> Death Valley </td>
   <td style="text-align:right;"> 11 </td>
   <td style="text-align:left;"> 01 </td>
   <td style="text-align:right;"> 52.5 </td>
  </tr>
  <tr>
   <td style="text-align:left;"> Death Valley </td>
   <td style="text-align:right;"> 12 </td>
   <td style="text-align:left;"> 01 </td>
   <td style="text-align:right;"> 52.7 </td>
  </tr>
  <tr>
   <td style="text-align:left;"> Death Valley </td>
   <td style="text-align:right;"> 13 </td>
   <td style="text-align:left;"> 01 </td>
   <td style="text-align:right;"> 52.9 </td>
  </tr>
  <tr>
   <td style="text-align:left;"> Death Valley </td>
   <td style="text-align:right;"> 14 </td>
   <td style="text-align:left;"> 01 </td>
   <td style="text-align:right;"> 53.0 </td>
  </tr>
  <tr>
   <td style="text-align:left;"> Death Valley </td>
   <td style="text-align:right;"> 15 </td>
   <td style="text-align:left;"> 01 </td>
   <td style="text-align:right;"> 53.2 </td>
  </tr>
</tbody>
</table>
]]

---

## Temperatures mapped onto y position

.center[
<img src="aesthetic-mappings_files/figure-html/temp-normals-vs-time-1.svg" width="70%" />
]

???

Figure redrawn from [Claus O. Wilke. Fundamentals of Data Visualization. O'Reilly, 2019.](https://clauswilke.com/dataviz)

---

## Temperatures mapped onto color

<br>

.center[
<img src="aesthetic-mappings_files/figure-html/four-locations-temps-by-month-1.svg" width="85%" />
]

???

Figure redrawn from [Claus O. Wilke. Fundamentals of Data Visualization. O'Reilly, 2019.](https://clauswilke.com/dataviz)

---

## Commonly used aesthetics

.center[
<img src = "https://clauswilke.com/dataviz/aesthetic_mapping_files/figure-html/common-aesthetics-1.png", width = 90%></img>
]

???

Figure from [Claus O. Wilke. Fundamentals of Data Visualization. O'Reilly, 2019.](https://clauswilke.com/dataviz)

---

## The same data values can be mapped to different aesthetics

.center[
<img src = "https://clauswilke.com/dataviz/aesthetic_mapping_files/figure-html/basic-scales-example-1.png", width = 90%></img>
]

???

Figure from [Claus O. Wilke. Fundamentals of Data Visualization. O'Reilly, 2019.](https://clauswilke.com/dataviz)

---

## We can use many different aesthetics at once

<br>

.center.move-up-1em[
<img src="aesthetic-mappings_files/figure-html/mtcars-five-scale-1.svg" width="60%" />
]

???

Figure from [Claus O. Wilke. Fundamentals of Data Visualization. O'Reilly, 2019.](https://clauswilke.com/dataviz)

[//]: # "segment ends here"

---
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## Creating aesthetic mappings in ggplot

---

## Getting the data

All examples will use the `temperatures` dataset:

.tiny-font[

```r
temperatures <- read_csv("https://wilkelab.org/SDS375/datasets/tempnormals.csv") %>%
  mutate(
    location = factor(
      location, levels = c("Death Valley", "Houston", "San Diego", "Chicago")
    )
  ) %>%
  select(location, station_id, day_of_year, month, temperature)
```
]

---

## We define the mapping with `aes()`

.small-font[

```r
ggplot(
  data = temperatures,
  mapping = aes(x = day_of_year, y = temperature, color = location)
) + geom_line()
```
]

.center[
<img src="aesthetic-mappings_files/figure-html/ggplot-temps-example-out-1.svg" width="55%" />
]

---

## We define the mapping with `aes()`

.small-font[

```r
ggplot(
  data = temperatures,
  mapping = aes(x = day_of_year, y = location, color = temperature)
) + geom_point(size = 5)
```
]

.center[
<img src="aesthetic-mappings_files/figure-html/ggplot-temps-example2-out-1.svg" width="75%" />
]

---

## We frequently omit argument names

Long form, all arguments are named:

.small-font[

```r
ggplot(
  data = temperatures,
  mapping = aes(x = day_of_year, y = location, color = temperature)
) + geom_point(size = 5)
```
]

Abbreviated form, common arguments remain unnamed:

.small-font[

```r
ggplot(temperatures, aes(day_of_year, location, color = temperature)) + 
  geom_point(size = 5)
```
]

---

## The geom determines how the data is shown

.small-font[

```r
ggplot(temperatures, aes(day_of_year, temperature, color = location)) + 
  geom_line()
```
]

.center[
<img src="aesthetic-mappings_files/figure-html/ggplot-temps-example5-out-1.svg" width="55%" />
]

---

## The geom determines how the data is shown

.small-font[

```r
ggplot(temperatures, aes(day_of_year, location, color = temperature)) +
  geom_point(size = 5)
```
]

.center[
<img src="aesthetic-mappings_files/figure-html/ggplot-temps-example6-out-1.svg" width="75%" />
]

---

## The geom determines how the data is shown

.small-font[

```r
ggplot(temperatures, aes(month, temperature, color = location)) + 
  geom_boxplot()
```
]

.center[
<img src="aesthetic-mappings_files/figure-html/ggplot-temps-example7-out-1.svg" width="80%" />
]

---

## The geom determines how the data is shown

.small-font[

```r
ggplot(temperatures, aes(month, temperature, fill = location)) + 
  geom_violin() + 
  facet_wrap(vars(location)) # make separate panel per location
```
]

.center[
<img src="aesthetic-mappings_files/figure-html/ggplot-temps-example8-out-1.svg" width="90%" />
]

[//]: # "segment ends here"

---
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## Important: `color` and `fill` apply to different elements

---

## `color` and `fill` apply to different elements

`color`<br>
Applies color to points, lines, text, borders

`fill`<br>
Applies color to any filled areas

---

## Many geoms have both `color` and `fill` aesthetics

.tiny-font[

```r
ggplot(temperatures, aes(month, temperature, color = location)) + 
  geom_boxplot()
```
]

.center[
<img src="aesthetic-mappings_files/figure-html/ggplot-color-fill-out-1.svg" width="80%" />
]

---

## Many geoms have both `color` and `fill` aesthetics

.tiny-font[

```r
ggplot(temperatures, aes(month, temperature, fill = location)) + 
  geom_boxplot()
```
]

.center[
<img src="aesthetic-mappings_files/figure-html/ggplot-color-fill2-out-1.svg" width="80%" />
]

---

## Many geoms have both `color` and `fill` aesthetics

.tiny-font[

```r
ggplot(temperatures, aes(month, temperature, color = location, fill = location)) + 
  geom_boxplot()
```
]

.center[
<img src="aesthetic-mappings_files/figure-html/ggplot-color-fill3-out-1.svg" width="80%" />
]

---

## Aesthetics can also be used as parameters in geoms

.tiny-font[

```r
ggplot(temperatures, aes(month, temperature, fill = location)) + 
  geom_boxplot(color = "steelblue")
```
]

.center[
<img src="aesthetic-mappings_files/figure-html/ggplot-color-fill-params-out-1.svg" width="80%" />
]

---

## Aesthetics can also be used as parameters in geoms

.tiny-font[

```r
ggplot(temperatures, aes(month, temperature, color = location)) + 
  geom_boxplot(fill = "steelblue")
```
]

.center[
<img src="aesthetic-mappings_files/figure-html/ggplot-color-fill-params2-out-1.svg" width="80%" />
]

[//]: # "segment ends here"

---

## Further reading

- Fundamentals of Data Visualization: [Chapter 2: Visualizing data](https://clauswilke.com/dataviz/aesthetic-mapping.html)
- Data Visualization—A Practical Introduction: [Chapter 3: Make a plot](https://socviz.co/makeplot.html#makeplot)
- [**ggplot2** reference documentation](https://ggplot2.tidyverse.org/reference/index.html)
- [**ggplot2** book](https://ggplot2-book.org/)
- [**ggplot2** cheatsheet](https://raw.githubusercontent.com/rstudio/cheatsheets/main/data-visualization.pdf)