https://medium.com/google-design/google-maps-cb0326d165f5

When I worked on Google Maps as a UX Engineer, one of the things I really wanted to be able to do was create prototypes that could synchronize animations with zoom. However the JavaScript Maps API has limited control of the zoom, so in order to have more control, I experimented with using HTML5 canvas to composite the tiles in a fully custom implementation.

To understand what makes smooth zoom challenging for modern map applications, it helps to first understand how the map is made, and how Google Maps (and most of the other) map clients work — you can search for the bolded titles to go straight there.