In 2025, the Spanish Supreme Court ruled that source code for a piece of software developed for a Ministry (the BOSCO tool) needed to have its source code released. Nowadays laws are being implemented as computer code; and for a democratic society to function as such, the public needs to be able to know both the letter of the law and the source code of the software used to enforce that law.

The BOSCO ruling sets an European precedent for algorithmic transparency and digital sovereignty.

A default web map takes data in latitude-longitude and displays it in spherical Mercator, which makes two different coordinate systems. But the internal workings of a mapping library require handling even more coordinate systems internally.

This talk is a deep technical view into how some web map libraries (Leaflet, MapLibre, OpenLayers, Gleo) handle coordinate systems internally, and how their different strategies affect performance in specific scenarios.