Web Standards

Education is not limited to just classrooms. It can be gained anytime, anywhere... - Ravi Ranjan (M.Tech-NIT)

Before we can start using D3 to create visualizations, we need to get familiar with web standards. The following web standards are heavily used in D3 so we will go over these concepts briefly:

  • HTML
  • DOM
  • CSS
  • SVG
  • Javascript

HTML

HTML = HyperText Markup Language

HTML is used to structure the content of the web page. The current version is HTML 5. It is stored in a text file with the extension ".html".

A typical bare-bones HTML example looks like this:

Example: Use D3 library from CDN


<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title></title>
</head>
<body>

</body>
</html>
            

Learn HTML from developer.mozilla.org

DOM

DOM = Document Object Model

When you write html code for your page, it gets converted to a hierarchical structure on the browser. Every tag in html gets converted to an element in the DOM with a parent-child hierarchy. It makes your html more logically structured. Once the DOM is formed, it makes it easier to manipulate (add/modify/remove) the elements on the page. Remember we had learnt in the first chapter that the first 'D' in D3 stands for Document. D3 gives you the tools to manipulate this DOM via your data.

Learn more about DOM from developer.mozilla.org.

CSS

CSS = Cascading Style Sheets

HTML gives a structure to the web page, while CSS styles your web page making it more pleasant to look at. It is a stylesheet language used to describe the presentation of a document written in HTML or XML (including XML dialects like SVG or XHTML). CSS describes how elements should be rendered on a web page.

Learn CSS from developer.mozilla.org.

SVG

SVG = Scalable Vector Graphics

SVG is a way to render images on the web page. SVG is not a direct image but is just a way to create images using text. As it's name suggests, it is scalable vector. It scales itself according to the size of the browser, so resizing your browser will not distort the image. All browsers support SVG except IE 8 and below.

Since data visualizations are visual representations, it is convenient to use SVG to render visualizations using D3.

Think of SVG as a canvas on which you can paint different shapes.

So to start off, create an SVG tag: <svg width="500" height="500"></<svg>

The default measurement for SVG is pixels, so you don't need to specify if your unit is pixel.

Now if you would like to draw a rectangle inside this SVG, draw it using <rect> :

Example: Square in SVG


<svg width="500" height="500">
    <rect x="0" y="0" width="300" height="200"></rect>
</svg>

You can draw the square using <rect> by applying same width and height attribute. Some of the other shapes that can be drawn in SVG include line, circle, ellipse, text and path.

Just like styling html elements, styling SVG elements is simple. Let's color the above rectangle in yellow. All you need to add is an attribute "fill" and specify the color.

Example: Colored Rectangle


<svg width="500" height="500">
    <rect x="0" y="0" width="300" height="200" fill="yellow"></rect>
</svg>

Learn more about SVG from developer.mozilla.org

JavaScript

JavaScript is a loosely-typed client side scripting language that executes in the user's browser. JavaScript interact with html elements (DOM elements) in order to make the web user interface interactive.

JavaScript implements ECMAScript standards, which includes core features based on ECMA-262 specification as well as other features which are not based on ECMAScript standards.

JavaScript knowledge is a prerequisite for D3.js. Visit JavaScript section to learn more about JavaScript.

Let's start with D3.js by setting up development environment in the next section.