Google+ is another OAuth 2.0 site so we, of course, need to get an application key as the first step to creating any visualization. This also means that we will need a return URL, so again we'll need to set up an HTTP server to run the visualization.
The first step is to log into https://code.google.com/apis/console using your Google account. Should you not have such an account, you can also create one from that page. Once on the site, you'll be presented with a giant button allowing you to create an application project. This console actually governs the access to all of Google's APIs, and there are quite a few.
Next, you'll be presented with a huge list of the various APIs. If you scroll way down, you'll eventually find Google+ (use the search, it will save hours of scrolling). Toggle the switch to the "on" position. You may need to agree to a couple of user agreements. Be sure to read the entire agreement as you always do.
The next step is to request a new key, as shown in...