How colour cycling in the browser can deliver pretty, fast map overlays

Colour cycling is an unlikely technology to find in modern web mapping, but when performance is key, we found it the best bet. For when Canvas and SVG are just too slow...

How colour cycling in the browser can deliver pretty, fast map overlays
mysociety.org

The genial part, from the article:

  So in summary, what we built does this:

  The server calculates the journey times and renders them to palette-based tiles.
  It then sends these to the client encoded in Base64, and with the initial bits up to the palette and   transparency chunks removed.
  At the client end, we have a pre-prepared array of 255 ‘starts’ of PNGs that we combine with the later parts   of the ’tiles’ from the tile server to make data URIs.
  When you drag the slider it combines the appropriate ‘start’ of a PNG with the bulk of the tile that has been   downloaded from the server, and assigns that to the src attribute of the tile.