USGS topographic map of Mount Rainier with contours, glaciers and named summits.

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Preparing the 3D view

Preparing lighting and the first complete frame…

Model scale

Relief ×2.5. same hill and contour vertices. T restores equal horizontal / vertical scale.

Contour interval 10 m · spot 89.4 m. Click the hill to check a height. Turn off “3D hill” and look from above for its contour map; the elevations stay the same.

Contours ↔ 3D terrain

Relate contour spacing and shape to the height and slope of a landscape, then distinguish a valley from a spur.

Drag to rotate. Hold Ctrl and scroll to zoom, or pinch on a touch screen.

Why it happens

A contour joins places at the same elevation. Closely spaced contours indicate a steep slope, while wider spacing indicates a gentler slope; their patterns reveal valleys, ridges and summits.

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USGS Mount Rainier topographic sheet, published in 1971. Contours connect equal elevations; close spacing marks steep slopes.

Try a comparison

Change Contour interval while keeping the terrain fixed. Compare tightly spaced and widely spaced contours and explain the difference in slope.

Reading the result

The same constructed terrain appears in both views, so changing the contour interval changes the map’s detail, not the hill.

A common misunderstanding

The V-shaped bend of a contour always points downhill.

Where a contour crosses a stream valley, its bend generally points uphill and upstream. Around a projecting spur, the bend points downhill. Follow the height labels and nearby drainage to distinguish the two; the shape of a single line without context can be misleading.

Cases

Adjust parameters

Contour interval10 m