Please note in the mapdata.js, there's a command: 'maxzoom':5.99 under the map.addLayer function.
There are reasons for limiting the zoom extent:
- It suits the geographical extent of our data, which focus on provincial granularity. Therefore, we don't need to go beyond that zoom level; and more importantly,
- Detailed processing of spatial data entails higher costs. Hosting and processing spatial data with zoom extent under 6 are completely free. More info on: https://www.mapbox.com/pricing/
For now, simply set the maxzoom below 6 for all map layers.