Skip to main content

--description--

The bar and scatter plot charts both plotted data directly onto the SVG. However, if the height of a bar or one of the data points were larger than the SVG height or width values, it would go outside the SVG area.

In D3, there are scales to help plot data. scales are functions that tell the program how to map a set of raw data points onto the pixels of the SVG.

For example, say you have a 100x500-sized SVG and you want to plot Gross Domestic Product (GDP) for a number of countries. The set of numbers would be in the billion or trillion-dollar range. You provide D3 a type of scale to tell it how to place the large GDP values into that 100x500-sized area.

It's unlikely you would plot raw data as-is. Before plotting it, you set the scale for your entire data set, so that the x and y values fit your SVG width and height.

D3 has several scale types. For a linear scale (usually used with quantitative data), there is the D3 method scaleLinear():

const scale = d3.scaleLinear()

By default, a scale uses the identity relationship. The value of the input is the same as the value of the output. A separate challenge covers how to change this.

--instructions--

Change the scale variable to create a linear scale. Then set the output variable to the scale called with an input argument of 50.

--hints--

The text in the h2 should be 50.

assert($('h2').text() == '50');

Your code should use the scaleLinear() method.

assert(code.match(/\.scaleLinear/g));

The output variable should call scale with an argument of 50.

assert(output == 50 && code.match(/scale\(\s*?50\s*?\)/g));

--seed--

--seed-contents--​

<body>
  <script>
    // Add your code below this line

    const scale = undefined; // Create the scale here
    const output = scale(); // Call scale with an argument here

    // Add your code above this line

    d3.select("body")
      .append("h2")
      .text(output);

  </script>
</body>

--solutions--

<body>
  <script>

    const scale = d3.scaleLinear();
    const output = scale(50); 

    d3.select("body")
      .append("h2")
      .text(output);

  </script>
</body>