Elevation profile: cut a cross-section of the terrain anywhere in Québec

A shaded-relief map shows the land from above. But many practical questions are asked side-on: how much does this trail climb? Does this forest road exceed the allowed grade? Does the hill hide the antenna? Until now, answering meant downloading tiles, opening GIS software and drawing a section. On Québec 3D, you now just draw a line.

The Explorer's new Elevation profile tool unfolds the relief along any line, wherever Québec is covered by airborne LiDAR. It is free, needs no account, and everything is computed in your browser.

What is an elevation profile?

It is a vertical cross-section of the terrain along a line. The horizontal axis shows the distance travelled from the start; the vertical axis, the ground elevation at each point. You read it like the silhouette of the landscape seen from the side: a terrace, a bank, a ravine or a cliff takes an instantly recognizable — and measurable — shape.

A profile is only as reliable as the terrain behind it. Here the source is the digital terrain model (DTM) derived from the MRNF's LiDAR surveys at 1-metre resolution: bare ground, stripped of vegetation and buildings.

Draw a profile in four steps

1. In the map panel, click “Elevation profile”. A drawer opens at the bottom of the screen.
2. Click on the map to set the starting point, then each bend of the line: the profile can follow a road, a riverbank or a trail, not just a straight line. On a phone, tap the map.
3. Finish with a double-click or the “Finish” button. “Undo point” removes the last vertex.
4. Hover over the curve (or slide a finger along it): a marker follows the matching point on the map, and the bottom line shows distance, elevation and local slope.

The tool also works in 3D: the line drapes over the relief, which helps place it precisely at the foot of a bank or along a ridge. The CSV button downloads the full profile — distance, latitude, longitude and elevation of each point — ready for a spreadsheet.

Reading the numbers

Above the curve, one line summarizes the profile:

• Length — the horizontal distance, measured on the Earth's sphere (the straight-line distance of each segment, added up).
• Elevation — the lowest and highest ground point along the line.
• Gain / loss — the cumulative climbs (+) and descents (−). So that micro-undulations don't inflate the total, a change only counts once it exceeds 1 metre from the last retained level.
• Average and maximum slope — as a percentage, measured over 5-metre windows. Handy reminder: 10% is about 5.7°, and 100% is 45°. A very steep maximum almost always flags a cliff, a retaining wall or an abrupt bank.

Bare earth or surface: two curves, two questions

Tick “Surface (buildings + forest)” and a second, green curve appears above the ground. It follows the surface model: the ground plus the height of the canopy and buildings. The gap between the two curves is what stands above the terrain — and the summary then shows the maximum height above ground, the tallest obstacle met along the line.

This double reading changes the kind of questions you can ask. The ground curve answers “how does the land rise?”. The surface curve answers “what blocks the way or the view?” — a 25-metre tree line on a ridge, a dense neighbourhood in the path of a radio link.

What it is good for

Hiking, cycling, cross-country skiing — Gauge the effort of a route before setting out: where the climbs are, how many cumulative metres, which ramp is steepest.

Civil engineering and planning — Check the grade of an access, spot a low point where water will pool, compare two road or pipe alignments, locate a culvert. The profile is the first move in any preliminary design.

Forestry — Assess a forest-road alignment or a harvest block against slopes, and read, with the surface curve, the stand height along a transect.

Telecommunications — Between two high points, the surface curve shows at a glance whether terrain or forest gets in the way: a first clearance check, before any propagation study.

Hydrology and riverbanks — Cutting across a valley, perpendicular to the stream, reveals the shape of the channel, the height of the banks and the extent of the floodplain. Across a lake whose bathymetry is built in, the profile even dives down to the bottom.

How it is computed

The profile is read directly from the same elevation tiles that draw the map: no computing server, no data sent anywhere. The line is sampled at up to 800 evenly spaced points, and each point is read at the level of detail that matches that spacing:

• a line a few hundred metres long is read at the finest level, roughly one point every 1.5 to 2 metres;
• a line tens of kilometres long is read more coarsely, at the scale of its spacing — there is no point reading every metre to draw an 800-point curve.

Between model cells, elevation is interpolated (bilinear) for a continuous curve with no staircase steps. As a result, a 20 km profile appears in a few seconds, even on a phone.

Limits worth knowing

This is not a land survey. The profile faithfully renders the LiDAR model, but an engineering decision rests on certified data and, where needed, a field survey. Unsounded water bodies carry the elevation of their surface at the time of the flight: a river shows up as a flat step, not as a channel. Finally, the surface curve is deliberately smoothed: it gives the envelope of obstacles, not the exact ridge of a roof.

The takeaway

A single line now turns Québec's LiDAR relief into a measured cross-section: elevation, gain and loss, slope and, optionally, the height of whatever grows or stands above the ground. It is the first in a series of free tools meant to make this public data directly useful — no software, no download, no account.