# Visualizations and the grammar of graphics

## Learning objectives

* Identify the importance of graphics in communicating information
* Define the layered grammar of graphics
* Demonstrate how to use layered grammar of graphics to build Minard's graph of Napoleon's invasion of Russia
* Practice generating layered graphics using [`ggplot2`](https://github.com/hadley/ggplot2)
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**April 8, 2020**

## Lecture Notes

### The important of data visualization
* Really helpful sometimes to visualize the data rather than to just observe the raw data
* Visualize patterns

### Grammar
* Must obey the rules of grammer to form a coherent **language**
* **[Grammar of Graphics:](https://cfss.uchicago.edu/notes/grammar-of-graphics/)** "The fundamental principles or rules of an art or science"
* `ggplot2` uses this grammar in R -> layered grammar of graphics

Example: Minard's map
* Utilizes line and color
* *Can we define this visualization using the grammar of graphics?*

### Building Minard's map in R
* `troops` and `cities` data frames representing different kinds of information
* Minard's grammar: troops (latitude, longitude, survivors, advance/retreat), cities (latitude, longitude, city name)
* layer, scale, coordinate system, faceting

*[Building Minard's map in R](https://cfss.uchicago.edu/notes/minard/) solutions on the CFSS website*

* **Layer** defines all the major visual elements
* **Scale** allows us to change the asethetic appearance of those elements