GeoAI Maps the Surface of 9.2 Million Kilometres of Roads
Most global road maps can tell us where a road is. Far fewer can tell us whether it is paved, how wide it is, or whether it might keep a relief convoy moving after a flood.
A new peer-reviewed study in Nature Communications shows how satellite imagery and deep learning can begin to close that gap. Researchers from Heidelberg University and HeiGIT mapped road surface type and estimated width across 9.2 million kilometres of the world’s critical arterial roads.
The result is not simply a more complete road inventory. It is an attempt to turn imagery into infrastructure intelligence.
From road lines to road condition
The team started with OpenStreetMap geometries for motorways, trunk, primary and secondary roads. It then analysed 3 to 4 metre PlanetScope imagery from 2020 and 2024 using a fine-tuned Mask2Former segmentation model.
The resulting dataset covers 95.5% of the selected 9.2 million-kilometre network. Nearly half of those roads previously lacked a surface classification. The researchers also found that OpenStreetMap tags for unpaved roads achieved only 26% average global accuracy in their human-validated comparison, often because attributes had not kept pace with development on the ground.

This is an important distinction. OpenStreetMap remains the indispensable geometry layer, while Earth observation provides a way to update physical attributes at scale. The two are complementary rather than competing systems.
A new layer for infrastructure decisions
Road surface data revealed a pronounced urban-rural divide. Urban arterial networks were more than 93% paved across all regions, while rural pavedness in Sub-Saharan Africa averaged 61.4%, compared with 97.2% in Europe and Central Asia.
The researchers also found that changes in pavedness between 2020 and 2024 correlated with human development after accounting for each country’s starting point. That does not prove that paving causes development, but it suggests that frequently updated road-condition maps could complement slower official statistics and coarse proxies such as night-time lights.
The most operational part of the work is a Humanitarian Passability Score. By combining estimated width and surface type, the framework distinguishes high-capacity supply corridors from narrow or weather-sensitive chokepoints.

For humanitarian teams, development banks and governments, that is potentially more useful than another global road centreline dataset. It begins to answer whether a mapped route is likely to support the vehicles and loads required during an emergency.
The resolution ceiling still matters
The authors are careful about the limitations. PlanetScope imagery cannot resolve individual lanes, so road width is a first-order estimate. Clouds, shadows, vegetation, moisture and seasonal changes can also create apparent deterioration or improvement where none occurred.
The passability score is not a live declaration that a road is open. It is a structural indicator that would still need recent weather observations, flood data and field verification before operational use.
There is also a licensing distinction. The derived vector dataset is available through the Humanitarian Data Exchange under a non-commercial Creative Commons licence, while the underlying Planet imagery cannot be redistributed.
Still, the strategic direction is clear. GeoAI is moving beyond extracting buildings and road geometry. The next valuable products will describe what infrastructure is made of, how it changes and what it can actually support.