Contour → Terrain Profile

Quick guide

Use cases, answers, and nearby tools

Compact below-tool notes that help first-run users and repeated visitors move faster without changing the main interface.

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How to use

Run a clean first pass

Pick a real terrain specimen — all 14 are real places rendered from SRTM elevation: Fuji’s cone, Taroko’s V-shaped gorge, Yosemite’s U-shaped valley, the incised meanders of the San Juan, the volcanic island of Guishan.
Drag the cutline or either endpoint and the cross-section redraws beneath it, with real distance in km and elevation in metres — plus the vertical exaggeration, the thing every printed profile does to you and almost never states.
Try the contour interval at ×½ / ×1 / ×2: the hill does not change, only how often it is sliced. Switch on line-art mode to check you are reading the lines and not the shading. Then try Reverse Quiz — read one profile and pick which of three contour maps produced it.

Examples

Real jobs this page helps with

V-shaped vs U-shaped: rivers and glaciers, side by sideCut across Taroko: a river saws downward and the profile is a narrow, deep V. Now cut across Yosemite: a glacier scoured the whole floor, so the bottom is flat and the walls stand near-vertical. One tool, two processes, no explanation needed.
The V of a contour points upstreamOn the Grand Canyon, run the cutline across any tributary. Every contour bends into a V and every point aims upstream — the most-tested rule in the syllabus, demonstrated by dozens of gullies at once.
A peak and a hollow look identical in contoursCrater Lake and Mt. Fuji are both nested closed loops. One descends inward, the other climbs. Two things separate them: whether the labelled heights rise or fall inward, and hachures — the short ticks drawn across a contour, always pointing downhill. This tool labels heights but does not draw hachures, so read the numbers, then cut a section and be certain.
How tight is tight? Read the slopeQingshui Cliffs rise almost 800 m straight out of the sea. Cut square across the cliff face and the gradient jumps to the steepest stretch here; cut at an angle and it reads low — the number follows your cutline, not the hillside itself.
A coastline is a contour lineGuishan Island sits in flat, contourless water, and its outline is labelled 0. An island is the fastest way to see that the shoreline IS the zero-metre contour.

FAQ

What people usually want to know

How do you read a contour map?

Three things carry most of it. Every point on one line is at the same height; tightly packed lines mean a steep slope and widely spaced lines a gentle one; and where a line bends into a V the point aims upstream, while a bulge toward lower ground is a ridge. This tool lets you draw a cutline and watch all three appear at once in the cross-section.

Why does the V of a contour point upstream?

Because a valley is cut into the hillside. To stay at one height, the contour has to run up into the valley and back out, and the upstream end is the higher one — so the bend must point that way. Every tributary on the Grand Canyon specimen shows it.

What is the contour interval, and what happens if it changes?

It is the height difference between neighbouring lines. The ground does not change: a smaller interval slices more often, giving more lines and more detail; a larger one leaves only the broad shape. The ×½ / ×1 / ×2 control lets you see exactly that on one hill.

What is vertical exaggeration, and why do profiles look so steep?

A profile is usually kilometres across and metres tall. Drawn true to scale, a mountain flattens into almost nothing — so the vertical axis is stretched, and that factor is the vertical exaggeration. This tool prints it: at ×4 the HEIGHT on screen is four times over-long, which is why the slope looks so severe. The real gradient is the figure in degrees beside it — do not multiply that by four.

How do you tell a peak from a hollow?

Both are nested closed loops and look nearly the same. Two things separate them: whether the labelled heights rise or fall inward, and hachures — short ticks drawn across a contour, always pointing downhill. This tool labels its index contours but does not draw hachures; compare Crater Lake against Mt. Fuji and the difference is immediate.

Is this real terrain data?

Yes. Every cell comes from open elevation data (NASA SRTM, with USGS 3DEP inside the USA), fetched as Tilezen / Mapzen terrain tiles via AWS Open Data and baked into static files served with the page. Nothing is hand-drawn or procedurally generated, and the contours are computed in your browser by marching squares from the very same grid the profile samples — so the map and the cross-section are necessarily the same ground.

Why is the summit height slightly below the published figure?

SRTM samples every 30 metres and a sharp summit gets averaged down; each specimen is then resampled to roughly 15–115 m per cell to frame its landform, so it is smoother still. Yushan reads about 3911 m here against a published 3952 m. That is the sampling limit of open elevation data; the tool shows it honestly rather than rounding up.

Exam figures are black and white — does practising on a shaded colour map teach the wrong thing?

It can, which is why there is a line-art mode. Hillshading and an elevation ramp look good, but they read the terrain for you — you may be judging relief from the shadows without realising you are not reading the contours at all. The “Line-art mode (exam style)” switch under the legend turns off the shading and the colour ramp, leaving black lines on paper exactly like a printed exam figure. The contours themselves do not change and neither does the cross-section: if you can still read it that way, you have actually learned it.

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