How to Find the Contour Interval?



How to Find the Contour Interval?

These index strains will be mentioned with their elevation. Discover the elevations of two adjoining index lines. The largest range shows the uphill rise. Locate the distinction between the two elevations.

A contour map includes contour traces of a given geographical region. To keep the contour map convenient and comprehensible to read, now not each contour line is marked with its elevation reading.

These marked or tagged strains are remembered or termed index contour Lines. In the above picture, the darkish traces with analyzing are index contour lines.

What is Contour Interval?

Generally, there are a number contour intervals for the a range of maps. Taking the location to be mapped, contour intervals are considered. In each map, on the right-hand backside side, the contour interval is described. The often utilized contour interval is 20 toes for a 1:24,000 map scale.

To calculate contour interval, we want to divide the distinction in elevation between the index contour traces through the range of contour traces from one index contour line to the next.

For example, if the distance 200 is divided via the quantity of lines, the place the range of traces is 5. The contour interval is equal to 200 / 5 = 40, or 40-unit contour intervals.

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Types of Contour Lines

There are three kinds of contour traces detected on a map,

  1. Index Contour Line
  2. Intermediate Contour Line
  3. Supplementary Contour Line

1. Index Contour Line

The darkish labelled strains are referred to as index contours due to the fact index contour ambitions to inform you an actual elevation at a specific factor in areas between the two contour indexes, permitting you to work outward, and therefore downward or upward, from there. The related elevations peak generally quit in zero for convenience, though on metric maps, they on occasion cease in four or 5.

2. Intermediate Contour Line

The last contours are named intermediate contours. These commonly fall in between the index contour lines. The Intermediate contour strains are finer than index contours and do now not have their elevations named on them.

There are primarily 4 intermediate contour lines between any two successive index contour lines.

3. Supplementary Contour Line

In some unique areas on a map, the traditional interval is occasionally too huge to characterize a huge alternate in elevation, such as on-level terrain, and therefore, greater half-interval contours are added. These sorts of contours are named supplementary contours or shape lines.

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Uses of Contour Intervals in Surveying

When a giant location is to be mapped in small piece of paper contour intervals are used. A greater contour interval is used for a massive vicinity and small contour interval for small area.
In a giant map, index contour traces are much less to hold it easy to examine the map easily. In this case, to discover out the intermediate factors elevation, contour intervals are used.
Earthwork estimations for any kind of shape like bridges, dams or roads can be observed out with the assist of contour intervals in a map.

Advantages of Contour Interval

  • It suggests the slope and dimension of distinct landforms on the map.
  • By searching at the contour intervals it is handy to calculate the a number of elevations of the landscape.
  • It can be utilized in drawing cross-sections of the unique points on the mapped area.

Disadvantages of Contour Interval

  • Contour fail to signify a few of the heights due to the hassle of the vertical interval.
  • Some of the landforms can't be represented with the aid of using contours. For instance coral reef, outcrop rock, and craters.
  • The contour approach is no longer utilized to signify comfort on a small-scale map as it might also doubtful a few details.

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Characteristics of Contour in Surveying

The primary attribute of the contour can be listed as follows:

  • The horizontal distance between any two contour traces shows the quantity of slope and varies inversely on the quantity of slope.
  • Two contours of one of a kind elevations in no way pass every different without in the case of an overhanging cliff.
  • Contours of assorted elevations by no means unite to structure a single contour barring in the case of a vertical cliff.
  • Contours that are shut to every different depict a steep slope whereas the contours drawn aside depict a mild slope.
  • The equally spaced contours depict a uniform slope. When the contours are drawn parallel, equidistant, and straight, such contours point out inclined aircraft surfaces.
  • A contour line have to shut itself however may additionally no longer always be inside the limits of the map itself.
  • Contour at any factor is perpendicular to the line of the steepest slope at that point.


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