Analysis – Elevation Contours

A contour line or isohypse joins points of equal elevation. Maps illustrated with contour lines are commonly used for topographic maps - they use contour lines to show valleys, hills, and the steepness or gentleness of slopes.

The contour interval (or equidistance) of such a map is the difference in elevation between successive contour lines - maps typically used for hiking, for instance, use a contour interval of 10 m, so they show contour lines at every multiple of 10 m.

A map with contour lines.

The elevation layers in SCALGO Live rely on coloring and shading to represent elevation. If you prefer to look at elevations through contour lines, you can enable the "Contours" layer in the "Elevation" section of the library and choose a contour interval on the slider. These contour lines can be particularly useful on top of orthophotos or other non-elevation layers, when you want to view the elevation information at the same time.

How precise are the contour lines?

The contour line layers in SCALGO Live have been computed from the raw elevation data. The contour lines need to be simplified to be useful, but they never deviate from the actual elevation by more than half the contour interval. That is, if you pick a point on a contour line in the layer with the contour interval slider set to 50 cm and perform a point query, the terrain elevation will not differ by more than 25 cm from the contour line elevation. (However, small peaks and sinks of less than 10 m² area are dropped entirely, and in areas with low-resolution source data some additional interpolation is necessary that can degrade this guarantee.)

Peaks and sinks

In addition to the contour lines themselves, you can also enable peaks (points of locally maximal elevation) and sinks (points of locally minimal elevation). This is done using the gear icon of the contour layer in the dock. Here, you can also switch to light contour lines, which are useful on top of dark orthophotos.

Contour lines with extrema (peaks and sinks).

Light contour lines on top of orthophotos

Downloading contour lines

Like many other layers, you can download data from the contour line layers by activating the Export Tool, drawing a rectangle or polygon, and then selecting a contour line layer.

In the vector output, the smooth contour lines will be approximated using polygonal curves (with some fixed precision). The elevation of each contour line is stored in a field Height.

An exception is export to the DXF format, as this format supports smooth curves. In DXF export, the smooth contour lines are preserved, and the elevation is stored as the z-coordinate of each vertex.

Relationship to workspaces

Contour edits let you edit the terrain inside a workspace using contour-line based tools. Since they need to be easily editable, these contour lines often look slightly different from the precomputed contour line layers. The format of contour line edits exported from a workspace is also different from contour lines you download from a contour line layer.

Workspace contour lines are computed for your workspace as part of the workspace analysis.   They are computed using the same algorithm and parameter settings as the national contour map, but reflect any changes you have made to the terrain inside the workspace.