A contour map is a representation of a three-dimensional feature using contour lines on a flat surface. It shows hills, valleys, and slopes and includes a title, scale, contour range, and legend. Contour lines connect points of equal value and have a constant contour interval. Index contours help interpret the map, and different features can be visualized based on the contour lines. It can be used for camping, city planning, meteorology, and geological studies.
A contour map, sometimes called a topographic map, is a representation of a three-dimensional feature using contour lines on a flat surface. The map shows a bird’s-eye view and allows people to view the hills, valleys and slopes that are being mapped. It usually includes the title, scale, contour range, legend, and whether it uses latitude and longitude coordinates or Universal Transverse Mercator (UTM) coordinates. This type of map can be useful in many activities, including camping, city planning, meteorology, and geological studies.
Contour lines are the main component of a contour map. They connect points of equal value, such as elevation, to create the asymmetrical circles and curved lines that make up the map. The cartographic standard provides that the contour lines are brown.
How contour lines on a flat map can be used to show a three-dimensional surface can be understood if you imagine a mountain cut horizontally with a flat sheet of paper. The outline of the mountain as it intersects the sheet of paper at a particular same elevation would form a contour line. A contour map essentially takes horizontal slices of the mountain at specific intervals and shows the contours of the slices on a sheet of paper.
The contour lines on the map always have the same difference in value, called the contour interval. The range is chosen by the person producing the map. For example, each line could represent 10 feet (3m) of altitude. The range remains constant, so a person reading the contour map can estimate the value of any point between two contour lines.
A contour map also contains index contours to help interpret the map. The index contour is a thicker contour line labeled in multiple places with the value of the line. For example, there might be unlabeled contour lines for every 10 feet (3 m) of elevation, but every 50 feet (15 m) might be a thicker line with the elevation labeled. There are typically four contour lines between each contour index unless there is a change in slope, in which case there would be more than one contour line for the same elevation.
There are several geographic features that can be visualized if you understand what a contour map shows. If the contour lines are close together, it indicates a steep slope, such as up a hill or mountain. A map with evenly spaced contour lines means that the slope is constant and, where there are few contour lines, it is relatively flat terrain. A closed circle indicates a hill and a closed circle with tick marks is used to indicate a depression. Contour lines will form a “V” shape that will point uphill along a stream on a map.
While a contour map is often used to map geographic features such as elevation, it can serve other purposes as well. For example, in meteorology, this type of map is often used to show temperature or precipitation. Another example is when geologists use contour maps to show the depth of a lake or even underground features.
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