We’re currently in the process of updating our set of world maps for MapBox to update data, improve visuals, and increase speed. Here’s what will change:

• Move from 24-bit PNGs to 8-bit PNGs with a 32-color palette

• Adjustments to labels to improve how different-sized countries are handled

• Additions of provincial and state labels that were missing in the previous version

After testing various palette sizes for efficiency and attractiveness, we settled on a maximum of 32 colors per image. This gives us a major file size reduction from full-color PNGs, while still giving us good flexibility for smooth text and lines. With our initial tests we had hoped that a palette with as few as 16 colors would be sufficient, but in practice it caused too many oddities and jaggy lines. Increasing the palette to 32 colors was a very small sacrifice in average file size, especially compared to our old tiles, and gave us the appearance we wanted.

The new tiles are approximately 75–80% smaller than the old ones, depending on map and zoom level. Here’s a graph showing the difference in file sizes. Notice how our average file size is now 50% smaller than our previous minimum file size.

While the update is happening you may experience some odd behavior, such as old tiles and new tiles loading on the same map. This happens because Amazon Cloudfront, which we use to serve all our MapBox maps, takes some time to refresh its cache. There are approximately 90 million new images for each tile set, and even with many servers and processes it will take us a few days to get everything into place.

If you’re using our World Dark tileset you should already be seeing the new tiles on most zoom levels. If you’re using World Light, expect the changes to show up soon. For more information on MapBox tiles and how to use them, visit MapBox.com.

Thanks again to David Gray and the Innovate team at the World Bank for funding some of this compression research.