In part 1 I covered the hard problems: COG multi-resolution, SDF raster smoothing, and Barbapapa topology-preserving Laplacian smoothing. Freddie could generate good-looking 10m land cover vector tiles. This post is about what happened next: killing the algorithm I spent a week perfecting, solving a surprisingly dumb storage problem, and wiring the tiles all the way through to the map SDK.

Barbapapa is dead

I killed Barbapapa a few weeks after shipping it.

Every product starts by depending on open source it doesn’t fully understand. That’s fine. It’s the whole point. You stand on the shoulders of people who solved problems you haven’t even encountered yet, and you ship. The dependency is invisible because it works.

Then the product grows, and you start noticing the edges. The upstream project makes choices you wouldn’t have made. The schema carries fields you don’t use. The routing engine takes a turn you can’t explain. The update process becomes a gamble: bump to the latest version and hope nothing changed in a way that breaks your use case. You’re accountable to your customers for software you treat as a black box.

Serving vector tiles from 10-meter resolution land cover data. What breaks when you 100x the input resolution, and how topology-preserving smoothing fixes the ugly parts.

Background

Freddie is our tile server for land cover data. It reads GeoTIFF raster files (pixels classified as wood, grass, built-up, water, etc.) and serves them as vector tiles or raster tiles over HTTP. Nothing fancy. Read pixels, make shapes, encode, serve.

The original setup used ESA WorldCover at ~100m resolution. Native resolution sits around z8 in Web Mercator, so serving z0–z8 tiles was straightforward. Sample pixels, run-length encode, merge adjacent faces of the same class, encode to MVT. Done. It just worked, and I didn’t think much about it.

Rewriting the Woosmap Maps SDK on top of a Mapbox GL JS fork, with a Google Maps-compatible API surface, built with Bun, and an experiment in offscreen rendering.

Why

The Woosmap Maps SDK depended on Mapbox GL JS. Then Mapbox changed the license. Version 2.0 moved to the Business Source License, not open source anymore. The last truly open version was 1.13.1 (December 2020). No more upstream bug fixes, no WebGL2 improvements, no new features. We were stuck on a frozen codebase.

Generating Mapbox GL GL style JSON from Python code instead of editing 3,000-line JSON files by hand. Hierarchical style resolution, a Django-style filter DSL, injection-based layer ordering, and a Go sprite generator called from Python via ctypes.

The problem with style JSON

A Mapbox GL GL style is a single JSON file that describes everything about how a map looks. Background color, road widths at every zoom level, label fonts, icon placement, landcover tints, building extrusion heights. All of it.