Use Mapbox vector tile rendering

[barbeau]

I thought that vector tile rendering would be enabled by default with Mapbox map tiles (vs. raster image tiles), but looking at the tiles on an LG G4 I'm not sure that is the case.

Here's an image of the tiles in USF Maps App on the left, and on the right is the OTP Android app with the Mapbox vector tiles:

Here's a close-up of the street names:

To me, the images on the right in OTP Android seem clearer - it looks like the tiles in USF Maps App are raster tiles, not vector tiles.

I found this link, which also seems to imply that a special plugin is needed to render vector tiles using Leaflet:
https://github.com/mapbox/awesome-vector-tiles/blob/master/README.md

@jmfield2 Can you confirm whether or not we're using Mapbox vector tiles?

[jmfield2]

According to the style, there are no raster sources on the streets map. The satellite layer is raster according to the style.

I thought using the mapbox api just meant all of the vector layers and styles were applied by mapbox, and rendered as a PNG - which implicitly means at least the final stage was raster.

I'm still looking into whether rendering the vectors directly using html5/canvas as suggested by the links would make the tiles clearer.

[jmfield2]

Just some comments - another library that implements webgl-accelerated vector tile rendering is OpenLayers, as an alternative to switching to mapboxgl.

A plugin to leaflet that also may work with work to implement the mapboxgl rendering is:
https://github.com/SpatialServer/Leaflet.MapboxVectorTile

Note the WIP PR #322