Contours, also known as isolines, are lines that connect points of equal value and are used to represent continuous phenomena. Isolines may have specific names depending on the phenomenon they depict. For example, when representing elevation, they are referred to as “contour lines,” while for atmospheric pressure they are called “isobars.” Precipitation isolines are known as “isohyets,” and those indicating equal temperature are called “isotherms.” Additionally, “isochrones” represent equal travel time across a surface.
Contours are particularly useful for visualizing and understanding the topography of a region. On a topographic map, contour lines show the elevation of the Earth’s surface, enabling identification of mountains, valleys, plateaus, and other landforms. They can also be employed to analyze the spatial distribution of various environmental variables such as precipitation, temperature, or atmospheric pressure.
Contour layer (meters above sea level).
In essence, contours are a fundamental cartographic tool for visualizing and analyzing geographic data on a map.
Accessing the Contour Tool
The process for generating isolines is similar across different data types. In this example, contour lines are generated using a Digital Elevation Model (DEM) as the input. The tool used is “Contour,” located at the following path:
Geoprocessing > Toolboxes > Spatial Analyst Tools > Surface > Contour
Tool Configuration
To properly configure the “Contour” tool, the following parameters should be specified:
- Input raster: Select the raster layer containing the values to generate isolines. For elevation, a DEM should be used; for precipitation or temperature isolines, use the corresponding raster layers.
- Output features class: Define the output location where the new contour line feature layer will be stored. This can be a folder or a geodatabase.
- Contour interval: Specify the vertical distance between successive contour lines. The interval should be chosen based on the raster’s resolution. For example, if the DEM has a 30-meter resolution, intervals smaller than 30 meters are not recommended.
- Base contour: This optional setting allows the user to specify a base elevation from which contours begin.
- Z factor: An optional parameter to apply a conversion factor if the elevation units need to be changed (e.g., from feet to meters).
- Contour type: This optional setting can be used to define the type of contour features and to limit the number of vertices per line, if needed.
Configuration of the “Contour” tool parameters.
