August 26, 2025
Contours vs. Breaklines, What’s the Difference?
Contours and breaklines are vector line features used to represent terrain elevation. Since both describe a terrain surface, they are commonly confused with one another, despite the fact that their creation method(s) and applications are very different. Contours delineate areas of equal elevation, while breaklines delineate changes in slope.
Tip: Want to easily create contours or breaklines? Global Mapper Pro® contains a host of advanced terrain editing and analysis tools, including options for creating vector features from a digital elevation model (DEM).
What is a Breakline?
Breaklines indicate a change, or break, in elevation or slope. They trace the edges of slope and curvature, defining the transition from one surface plane to another. These vector lines outline edges and changes in a terrain surface, such as hills, plains, and ponds, to communicate the overall shape. Breakline elevation varies from vertex to vertex and often cuts across variances in elevation, making them different from contour lines.
How to Create a Map with Breaklines
Automatic breakline creation requires Global Mapper Pro and a loaded digital elevation model. Accessed from the Analysis menu or toolbar, the Automatic Breakline Generation tool contains three methods for breakline creation:
Tip: Use the Slope Shader to visualize the terrain by slope instead of elevation.
Find Breaklines at Slope Region Boundaries analyzes slope throughout a dataset to identify the edges of flat areas based on a user-defined slope threshold. Any value under the entered threshold is considered a flat area in this analysis. This method works well for identifying flattened areas, such as those on water and building sites.
Find Breaklines Around Edges of Regions with Similar Slopes works with a curvature value threshold to outline areas below the entered threshold value. Curvature measures the curve or deviation from a straight line at each location throughout the terrain dataset. This breakline creation method generates a standard curvature grid as a background process and uses this grid to identify closed contour lines at the threshold curvature value.
Find Breaklines at Any Surface Break generates breaklines based on the selected curvature method or slope. The Edge Detect Threshold and Edge Connect Threshold sliders determine how sensitive the breakline identification is and how identified lines along inconsistent edges are handled. This setting can also be used to extract curbs, as outlined in this other blog: Extracting Curbs as Breaklines.
What is a Contour Line?
Contour lines are what you see in a topographic map. A type of isoline, contours connect points of the same elevation value throughout a dataset. Typically, contour lines have a set vertical interval so that their horizontal spacing reflects the local slope characteristics, and changes in elevation are shown with labeled lines on a 2D or 3D map. This means that when contours are closer together, the area they represent is steeper. Created in Global Mapper, contour lines are 3D features where each line holds a single elevation value, and when followed, each line will return to its starting point to make a closed contour, or end at the edge of the dataset.
How to Create a Map with Contour Lines
In the standard version of Global Mapper, contour lines can be created from a digital elevation model; however, Global Mapper Pro enables users to create contours directly from point cloud data. With a couple of clicks in Global Mapper, contour lines at a user-set interval can be generated from any loaded elevation model. Perfect this workflow by learning more tricks for creating a contour map.
Iso-Height Areas
While contours are usually represented as lines, Global Mapper’s Contour Creation tool provides the additional option to create iso-height areas, or areas drawn at a specific elevation. This setting in the contour creation dialog transforms contour lines into polygon/area features at their prescribed elevations, which appear as planes stacked on top of each other when rendered in the 3D Viewer.
Create Points at Highest and Lowest Locations
An additional analysis process in the contour creation tool identifies local high and low points by identifying a specified number of concentric, or nested, contours. Additional parameters stipulating a required minimum distance between identified spot heights can be added, but the peaks and depressions identified are based on the contour lines generated by Global Mapper.
In the end, both contours and breaklines can be created in Global Mapper Pro from terrain data, and both describe the shape of the terrain. Contours do so by connecting equal elevation values, while breaklines analyze curvature and slope to outline or trace larger changes in the overall terrain.
If you would like to explore contour and breakline creation in Global Mapper Pro, download a 14-day free trial today! If you have any questions, please contact us.
