Twenty years ago, launching a road project began by sending a survey crew to measure the ground, stake by stake, for weeks. Today, much of that work already exists — free of charge — as a LiDAR digital terrain model. The starting point of a project has changed in nature.
Civil engineering lives on relief. Every slope, every hollow governs how water flows, how vehicles climb, how foundations rest. Having an accurate DTM before even setting foot on site does more than save time: it shifts decision-making upstream, where correcting costs the least.
Earthworks: balancing cut and fill
Designing a road means constantly trading off what you dig out (cut) against what you bring in (fill). Hauling earth is expensive; the ideal is to balance the two on site. From a LiDAR DTM, an engineer computes earthwork volumes for several alignments in a few hours, compares them, and keeps the one that minimizes soil movement — before an excavator touches the ground.
Drainage: following the water before it decides
Water doesn't consult the plans; it follows the slope. A fine terrain model lets you trace flow paths, delineate the watersheds that drain toward a culvert, and estimate the flows to evacuate. Undersizing a drainage structure means scheduling a local flood at the first major storm. LiDAR brings these paths to light where the eye sees only a flat field.
A one-metre difference in elevation, invisible on the ground, can decide whether a neighbourhood drains east rather than west. The DTM reveals it.
Corridors: siting linear infrastructure
Power lines, water mains, bike paths, railways: every linear infrastructure seeks the best compromise between slope, length and obstacles. By overlaying the DTM (the ground) and the DSM (the surface, with vegetation and buildings), you spot the conflict points — a woodlot to cross, a bank too steep — and optimize the alignment at the scale of the kilometre as well as the metre.
Urban planning and land use: a common foundation
At the scale of a municipality, LiDAR relief serves as a shared reference layer. It feeds land-use plans, buildable-slope analysis, stormwater management, solar-exposure assessment, 3D modelling of neighbourhoods. Because the data is open and uniform across the whole territory, a small municipality has access to the same foundation as a large city — a levelling up that is rare in geomatics.
This use connects directly to flood-zone mapping and the monitoring of ground movements, two major planning issues in Québec.
A concrete preview
Find an intersection, a quarry or a sloping neighbourhood, and observe the exact relief an engineer would work from — at the scale of a local project, then zooming out across the whole region.
Explore a site in 3D →A limit to keep in mind
A model does not replace the field. LiDAR gives a remarkable basis for study, but detailed design still requires a certified land survey, geotechnical boreholes, a site visit. Open data saves time and reduces upstream risk; it does not sign off the drawings. That, in fact, is the point of our Terms of Service: relief to explore and understand, not an engineering document.
The takeaway
LiDAR turned relief from data you go and fetch into data you already have. For civil engineering and planning, that means designing earlier, comparing more scenarios, and spotting flow or earthwork problems while they are still only lines on a screen.