# Announcements

• Assignment 3 due 11:59 MST on Tuesday, 2019-09-10, 11:59PM MST.

• Assignment 4 posted.

• Assignment 2 solution discussion.

# Lecture 6: d3 scales

In this lecture we will learn about one of the most important ideas in building data visualizations effectively, which is the use of transformations to encode the process of going from one space to another. In your Assignment 3, you have already been asked to create transformations from one space to another. To build your scatterplot, you will need to have transformed the space of SATM scores to the space of X coordinates, for example.

D3 has an extensive “scale” library. In d3, a “scale” is an object that encodes one such transformation in a particular way. But before we study d3 scale objects, let’s consider the previous simple example more explicitly:

## Quiz

1) You have data from SATM scores, and you want to give each SAT score a position in x coordinates in an SVG that goes from 0 to 500.

Write the following function:

   function convert(satm) {
var result = ...; // write this
return result;
}


2) You have data from ACT scores (which range from 1 to 36), and you want to give each ACT score a color, such that low ACT scores are encoded in red, and high ACT scores are encoded in green. Remember that, for now, we will be using values between 0 and 255 to encode the amount of red, green, and blue.

   function convert(act) {
var r = ...; // write this
var g = ...; // write this
var b = ...; // write this
return "rgb(" + r + "," + g + "," + b + ")";
}


3) You have data from CO2 concentration in the atmosphere around Mauna Loa (which ranges from 313ppm in 1959 to 360ppm in 1997), and you want to convert it to y coordinates. Write the following function:

   function convert(ppm) {
var result = ...;
return result;
}


# D3 scales

• Linear scales
• What do they do
• More than numbers
• You could have invented them
• Log scales
• and others
• Interpolators