Contour Intervals: Its Uses in Contour Surveying And How To Read It

A drawn line on the topographic maps indicating ground elevation or depression is said to be a contour line. On the other hand, a contour interval denotes the vertical distance or the existing difference in elevation between the contour lines. The increasing number of specific contour lines is an indication of the increasing elevation of the terrain. So, how do the contour intervals play a role in contour surveying? The remaining text will clear this question.

 

The contour surveyors use the contour intervals for mapping a large area on paper during contour surveys. They use a higher contour interval for the larger areas and small contour intervals for the smaller areas. With the help of contour intervals, the needed Earthwork estimates for any structure types like bridges, roads, or dams can be located on a map. Hence, engineers and architects can make effective use of during planning and designs.

Contour intervals are meant to calculate an area’s vertical elevation in the same way how the horizontal distances are calculated, so the contour intervals are regarded as the horizontal equivalent.  

Index contour lines are less in a large map, so the engineers and architects can read the contour surveyed map easily. Herein, contour intervals are used for finding out the elevation of the intermediate point.

The contour lines show the Earth’s shape. A single contour line marking an equal elevation line indicates if the contour line is measuring an elevation of 1000 feet above the average sea level, then all the points are above 1000 feet above the average sea level along that line.

Never do the contour lines cross, since a point on the map is incapable of having two different elevations at the same point in time. The farthest appearing contour lines on the map mean the earth's slope is smoother. The closer appearance of contour lines means the terrain will be more inclined.

Precipice occurs where the contour lines are getting very close. With the relief being a vertical cliff, the contour lines almost start coming together and seem like they are merging. Pending cliffs could have one line crossing over the other, but this is the one and only time for the lines to cross, and one line appears as dotted.

While reading, the engineers and architects are aware that the smaller cliffs could occur in between the contour lines, also in the areas having smooth slopes. For instance, a 15 feet high cliff, along a flow channel or else because of minor faults would not necessarily show whether the cliff is lying between two contour lines, specifically if they are having a longer contour gap.

A contour map comprises contour lines of a particular geographical region. Every contour line is marked with elevation reading for keeping the contour map easy to read and simple. In contour surveying, the contour interval is the vertical distance or else the prevailing difference in the elevation between the two contour lines in a topographical map. Generally, for different maps, the contour intervals are different. By considering the area size to be mapped, the assumptions are made for contour intervals. In all the maps, the contour intervals are specified on the right-hand bottom.

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