Tasting the Sourdough

The useful part

I'm supposed to write a full report about my attendance at State of the Map 2026. There are so many materials to discuss, especially the technical ones, and I'm already still stuck on day one already. If you check my latest OSM Diary entry in my State of the Map 2026 series, you'll see that my writing stopped rather abruptly at Jake Low's talk, titled "Sourdough and Layercake." It was a very interesting talk.

How it works

• In fact, while watching it live through the Venueless platform, I had already started thinking about some projects that I wanted to build on top of Sourdough.
• We can emphasize one aspect while pretending that everything else is "not important" and simply not showing it at all.
• We can selectively show some data layers and hide the rest.
• So instead of continuing to write that report, I started tinkering with Sourdough immediately.
• The cool thing about vector maps is that they are so easy to customize on the client side.

What to take from it

Arguments over which value a place=* tag should have (because some place values are prioritized for rendering over others). They aren't rendered because their icons clash with other POIs. I've seen plenty of serious battles over OpenStreetMap edit wars whose underlying reason seems to be rooted in the "battle for dominance" in the OSM Carto raster map.

Example or evidence

• When two or more POI coordinates are too close to each other, the renderer has to choose which one gets priority and which one gets hidden.

Details worth keeping

The never-ending flipping of highway classifications.