Editing the Terrain – Contour Edits

Workspaces let you change the terrain model and observe the effects on the analyses. This section discusses the powerful contour-based editing tools. For an overview of the process please consult the introduction page.

Contours are curves with a given elevation. They can be closed curves (for instance when modeling a basin or a hill), open curves (when modifying only part of a hillside), or even points (to specify the elevation at a single location only). Scalgo Live automatically interpolates the terrain elevation based on your contours.

Unlike the features created with the traditional tools, contours work in combination. A group of contours that together modifies your terrain is called a contour group in Scalgo Live. While creating or editing a contour, the contour group that it belongs to is indicated with a dashed yellow outline.

By their very nature, contours do not touch or intersect each other. Scalgo Live enforces this condition for contours in the same contour group.

You can create contours using the four contour tools in the Contours section of the workspace edit panel. The first three tools allow you to create or import contours, while the last tool enables you to extract contours directly from the terrain model.

Closed contour at a fixed elevation. Use this tool to model a basin or a hill that lies entirely inside your workspace. In "automatic mode", the elevation of the contour is taken from the terrain at the first point you click during drawing. Alternatively, you can specify the desired elevation before drawing the curve. (In either case you can later modify the elevation using the select tool.)

Note that when automatically picking the elevation, it is taken from the current terrain, that is, including all the terrain edits you have already made. A good strategy to use the automatic elevation assignment is therefore to create contour groups inside-out, that is, starting with the innermost contours.

To avoid a sharp edge (vertical wall) at the outer boundary of your contour group, you can add a blending area to the contour group. Inside the blending area, Scalgo Live blends between the existing terrain and the elevation determined by your contour lines, leading to a smooth transition.

To add a blending area to your contours, select the outermost contour line, and use "Blending area at distance" from the right sidebar (you may want to modify the distance at which the blending area will be created). The same action, with a few preset distances, is also available by right-clicking on the outermost contour line and selecting "Add blending area".   

Once a blending area has been created, you can edit the outline of the blending area like any other feature.   You can also delete it normally if you don't want to use it any longer.

If you find it more convenient to start your design by first delineating the area that will be affected by the contour line design, then you can start your drawing by drawing a blending area directly first.  To do this, select the Closed contours tool, but then right-click on the map and select "Draw a blending area". (Don't be surprised if the drawn area has no effect on the terrain - as soon as you add contour lines inside the blending area, this will change.)

A point contour simply specifies an elevation in a single location. They are typically used to mark extrema inside the innermost closed contours, but can also help to make sure your design meets certain given elevation constraints.

You can also create point contours outside any existing contour group. In this case, Scalgo Live automatically creates a new contour group consisting of a blending area and your new point.  You can then edit the blending area to meet your design.

You can add more point contours to quickly sketch a landscape design.   You could start by adding points at the extrema and refining with additional points until you are satisfied with the result.

An open contour specifies the elevation along a path. If you draw an open contour outside your existing contour groups, Scalgo Live automatically creates a new contour group consisting of a blending area and your new open contour.

When you want to model a hill side without having to model the entire hill, you want to draw only those parts of the hill's contours that are of interest to you.  After drawing the first open contour, edit the blending area to cover the area you are redesigning. (Alternatively, start by drawing the blending area using a right-click in the Closed contours tool as described above.)  Then draw open contours that start and end close to the boundary of the blending area, and therefore divide the area of the contour group into individual regions. Within each region Scalgo Live interpolates between the neighboring open contours.

The last contour tool is meant for extracting contours from the workspace terrain model. After you draw a polygonal boundary for your new contour group, Scalgo Live extracts lines at the chosen elevation interval from the current terrain (that is, with all your other modifications applied). You can then add, delete, and modify contours to modify the terrain.

Instead of drawing a boundary, you can also drag a vector file (GeoJSON, GeoPackage, Shapefile, Tab, DWG) with a single polygon into this tool.

You can import contours from a vector file, please consult the section on importing workspace edits for details.

If you have edited workspaces using contour lines before late 2025, you may have used contour group boundaries, recognizable as a dashed black curve, and there may be open contour lines that start and end on this boundary.

These old designs are still valid, but if you want to edit such a design further, then you will find it easier to convert them to the new version of the tools.

In the example above, select the dashed black contour boundary, and choose Convert to blending area from the right sidebar.

On the other hand, if your old design already has a blending area (so you have both a dashed black and a dashed blue curve), then select the dashed black contour boundary and simply delete it.

Often you may want to operate on all the contours that form some object in your design at once. 

You can move (translate) the entire contour group by holding the Shift-key and then dragging the yellow dashed line that is shown around your selected contour group.

You can delete an entire contour group from the right-click menu of any contour line.

Finally, you can export all the contours of a contour group from the same right-click menu.

It is often helpful to be able to see contour lines of the current terrain. While in any of the contour drawing tools (the first three contour tools), you can right-click anywhere in your workspace and ask for a contour line at this and nearby elevations.

Scalgo Live will show the resulting contour line as a thin blue line, an auxiliary contour. You can create arbitrarily many such auxiliary contours, clear them individually (by right-clicking on it) or all at once (right-click anywhere).

When you draw a contour in Scalgo Live, you will be drawing a smooth curve, because in natural terrains contour lines do not normally have sharp turns. When importing polygonal features from external software, on the other hand, Scalgo Live honors the imported geometry and creates polygonal contours. You can convert between the two representations using the right-click menu on the contour line (Convert to polygon and Convert to smooth curve). The conversion will fail if it would create a curve that intersects other contours of the contour group - in this case you may have to modify the curve first, delete some of its points, etc.

It could sometimes be useful to work with contour groups that overlap each other. For instance, you might first have modeled a basin using contours, then modified the basin using simple edit features, and then traced the resulting terrain model to obtain new contours that you can edit again.

Scalgo Live permits contour groups to overlap (while the contours inside a single contour group must never touch or intersect). To draw a new contour group on top of an existing one, you cannot use the contour tools normally - Scalgo Live would automatically add the new contour to the existing contour group. Instead, use the right-click menu while inside the contour drawing tool, and select Start new contour group. Drawing will then start and you can draw the new contour normally, creating a new contour group for it.

You can also take a contour line from an existing contour group and select "Convert to new contour group" from its right-click context menu (in the Select tool). This will remove the contour from its current contour group and create a new contour group for it.

In the opposite direction, you can merge contour groups, as long as their contour lines do not cross or touch.  Select a contour line from each of the contour groups you wish to merge, then use "Merge contour groups" from the right sidebar or the context menu.