Elevation Profile: How to Create and Read a Terrain Profile from a DEM
An elevation profile — also called a terrain profile or path profile — is a graph of ground elevation against distance along a line. Draw a line across a map, sample the height of the ground under it, and plot height on the vertical axis against distance on the horizontal one. It is the quickest way to see what a route, a slope or a section of a site actually does, and it is the first check most people run on a new surface. This guide explains how a profile is built from a DEM, what to read off it, and the three things that most often make it mislead.
How a profile is made from a DEM
The line is walked from start to end and the DEM is sampled along it. Each sample has a station — its horizontal distance from the start — and an elevation. Join the samples and you have the ground line.
The sampling interval matters less than people expect, as long as it is no coarser than the DEM cell. Sampling much finer than the cell adds points, not information: the surface between cell centres is interpolated, not measured.
What to read off a profile
A profile carries more than a shape. The numbers below come straight from the samples, and each answers a different question about the line.
| Figure | What it is | What it is used for |
|---|---|---|
| Plan length | Horizontal distance along the line | Chainage, map distance, quantities per metre |
| Slope length | Distance following the ground | Fencing, pipe, cable, haul distance |
| Minimum and maximum elevation | Lowest and highest ground on the line | Clearance, pump head, sight obstructions |
| Total ascent and descent | Sum of every climb and every drop | Effort of a route; fuel and cycle time on a haul |
| Average slope | Net height difference ÷ plan length | Overall grade between the two ends |
| Maximum slope | Steepest stretch between samples | Whether a vehicle, a drain or a path can use it |
Average slope hides the steep part
A line that climbs 30 m and drops 30 m has an average slope of zero and is not flat. Average slope only compares the two ends. For anything that has to travel the line — a truck, water, a person — read total ascent and descent for the effort and maximum slope for the limit.
Vertical exaggeration
Most profiles are drawn with the vertical scale stretched, because real ground is far longer than it is high and a true-scale drawing of a long line looks like a flat line. Exaggeration makes relief readable — and makes every slope look steeper than it is. A 10% grade drawn at 10× exaggeration looks like a cliff.
Read angles only from a profile at 1:1, or from the slope figures. If a drawing is exaggerated, the factor belongs in its title block.
Two surveys on one profile
A profile becomes a comparison tool when two surfaces are sampled along the same line: the ground before and after excavation, a design against the as-built survey, this month's stockpile against last month's. The gap between the two lines at any station is the depth of cut or fill there.
It is a check, not a quantity. A profile shows one line; a volume needs the whole area. Use the profile to see where the surfaces differ and a volume calculation to say by how much.
What makes a profile mislead
The surface type comes first. A profile over a surface model that includes vegetation and buildings shows canopy and roofs, not ground; for ground work, sample a bare-earth model. Resolution is second: a 30 m DEM cannot show a 5 m bench or a ditch, however finely the line is sampled. And the vertical datum is third — two surveys in different datums show a constant offset that looks like a real change.
Elevation profiles in STREAM
In STREAM, select a line you have drawn on the terrain and click Profile. The Section Profile panel plots the ground under the line and lists its distance, minimum and maximum elevation, average slope, total ascent and descent and 3D length. Moving the cursor along the graph marks the same station on the terrain view, and a click pins it, so a point on the profile can be found on the model.
The profile is drawn at 1:1 — no vertical exaggeration — and the mouse wheel zooms along the distance axis. Add Terrain Scenario overlays a second survey on the same line in its own colour. Export writes the profile as a CSV table or as a DXF profile drawing. If the terrain is edited while the panel is open, the profile updates.
For quantities rather than a single line, the cross-section tool cuts a section at every station along an axis and totals cut and fill with a volume table.
Frequently asked questions
What is an elevation profile?
A graph of ground elevation against distance along a line: height on the vertical axis, distance from the start on the horizontal one. It is also called a terrain profile or path profile.
How do you create an elevation profile from a DEM?
Draw a line over the DEM, sample the elevation under it at regular stations, and plot elevation against distance. In STREAM, select a drawn line and click Profile; the graph and its figures appear in the Section Profile panel.
What is the difference between an elevation profile and a cross-section?
A profile follows one line and shows the ground along it. A cross-section set cuts many sections at right angles to an axis, at a fixed interval, and is used to compute earthwork volumes between them.
What is vertical exaggeration?
Stretching the vertical scale of a profile so relief is visible on a long line. It makes slopes look steeper than they are, so angles should be read at 1:1 or from the slope figures, never from an exaggerated drawing.
Why is the average slope of my profile so low?
Because average slope only compares the two ends of the line. A route that climbs and then drops can average zero. Use total ascent and descent, and the maximum slope, to describe what lies between.
Can I compare two surveys on one profile?
Yes. Sample both surfaces along the same line and plot them together; the gap at each station is the cut or fill depth there. In STREAM, Add Terrain Scenario overlays a second survey on the open profile.
Draw a line and read its elevation profile in STREAM
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