cdnjs is a free distributed JS library delivery service.
D3.js is a JavaScript library for producing dynamic, interactive data visualisations in web browsers.
Google Analytics is a free web analytics service that tracks and reports website traffic.
HTTP Strict Transport Security (HSTS) informs browsers that the site should only be accessed using HTTPS.
Leaflet is the open-source JavaScript library for mobile-friendly interactive maps.
Netlify providers hosting and server-less backend services for web applications and static websites.
Open Graph is a protocol that is used to integrate any web page into the social graph.
Unpkg is a content delivery network for everything on npm.