Quebec Built Its Own Satellite Land Map — Here's How It Stacks Up

Land-cover maps are satellite images that label every patch of ground as a specific thing: forest, farm, city, water, or wetland. Quebec built one of its own called COTQ, which works at 10-meter resolution — meaning each pixel covers a square about the size of a small house. The point was to track, year by year, what land is being used for and how much green space is being paved over. Now researchers have put it head-to-head against three global competitors: ESA WorldCover, ESRI LandCover, and Google DynamicWorld.

The team didn't invent a new mapping technique. Instead, they tested how the maps behave. They translated all four into a single shared set of labels, then checked how well the shapes and edges of forests, fields, and towns lined up. They also measured how distinguishable different surface types are in the raw satellite light data, and they manually inspected the spots where the maps disagreed, using photo interpretation to see which one was right.

The test covered eight satellite tiles spread across Quebec's climate zones, from temperate forests in the south to treeless tundra in the far north. COTQ turned out to be most similar to ESA WorldCover. But real, systematic gaps appeared for cities, wetlands, and bare rocky surfaces covered in moss or lichen — mostly because each product defines those categories differently and prioritizes different things.

So why does this matter beyond Quebec? Because these maps are quietly used to decide where wetlands get protected, where flooding is likely, where farms can expand, and whether a city is sprawling onto good soil. When two maps label the same field differently, policy can change. This study doesn't crown a winner — it explains exactly where each map can be trusted and where a human should double-check.