Learning D3.js Mapping: Build stunning maps and visualizations using D3.js

Technically, most of the content we will craft can render directly in the browser without the use of a web server. However, we highly recommend you not to go ahead with this approach. Running a web server in your local development environment is extremely easy and provides several benefits:

For our choice of the web server and other tools in our toolbox, we will rely on a Node.js package named http-server. Node.js is a platform built on Chrome's JavaScript runtime, which is used to build fast, scalable network applications. The platform includes Node Package Manager (npm), which was created by other members of the vibrant Node.js community and allows the developer to quickly install packages of prebuilt software.

To install Node.js, simply perform the following steps:

To test the installation, type in the following in the command line:

node –v
v0.10.26 # or something similar should return

Now that Node.js and npm are installed, we can proceed to install the web server. When the web server is installed globally with the –g command, it becomes easily accessible throughout the system.

Once on the command line, enter the following:

npm install -g http-server

You can quickly verify the package was installed by typing the following:

http-server

Then open your web browser to http://localhost:8080. The browser should display a list of all the files in the directory from where you initiated the command.

Go to https://github.com/climboid/d3jsMaps and either clone the repo, if you are familiar with Git cloning, or simply download the zipped version. Once it is downloaded, make sure to extract the file if you have it zipped.

Use the command prompt or terminal to go to the directory where you downloaded your file. For instance, if you downloaded the file to your desktop, type in the following:

cd ~/Desktop/d3jsMaps
http-server

The last command will launch the simple server we installed previously for the supplied sample code. This means that, if you open your browser and go to http://localhost:8080/chapter-1/example-1.html, you should see a map of Europe, similar to the one shown earlier.

It's time to open the developer tools. On the top-right corner of the browser, you will see the icon as shown in the following screenshot:

This icon opens a submenu. Click on Tools. Then click on Developer tools. A panel will open at the bottom of the browser, containing all the developer tools at your disposal.

Within developer tools, you have a series of tabs (Elements, Network, Sources, and so on). These tools are extremely valuable and will allow you to inspect different aspects of your code. For more information on the Chrome developer tools, please go to the link https://developer.chrome.com/devtools/docs/authoring-development-workflow.

Since we are going to focus on the Elements tab, click on it if it is not already selected.

You should see something similar to the preceding screenshot; it will have the following code statement:

<svg width="812" height="584">

If you click on the SVG item, you should see it expand and display the path tag. The path tag will have several numbers and characters tied to a d attribute. These numbers are control points that draw the path. We will cover how the path is drawn in the next chapter and how path tags are used to create maps in Chapter 4, Creating a Map and Chapter 5, Click-click Boom! Applying Interactivity to Your Map.

We also want to draw your attention to how the HTML5 application loads the D3 library. Again in the Elements tag, after the SVG tag, you should see the <script> tag pointing to D3.js and topojson:

    <script src="http://d3js.org/d3.v3.min.js" charset="utf-8"></script>
    <script src="http://d3js.org/topojson.v1.min.js"></script>

If you click on the path located inside the SVG tag, you will see a new panel called the CSS inspector or the styles inspector. It shows and controls all the styles that are applied to a selected element—in this case the path element.

These three components create a D3 visualization:

Creating maps and visualizations using these three components will be discussed and analyzed throughout the book.