Creating interactive email treemaps using the Nylas Email API involves visualizing categorized email data in a rectangular format to enhance email management. The process begins with setting up a Nylas account and retrieving emails via Postman using the Nylas Email API. Emails are categorized into groups such as internal status updates, broadcasts, and external emails, using specific regex patterns. The visualization is built using FoamTree, a JavaScript library that generates treemaps with hierarchical data representation. The code and setup details are provided, including integrating the treemaps into a web application with Node.js and parcel bundler. The final product is an interactive visualization that can be accessed through a browser, offering an innovative way to organize and display email data.