What Is Contour Interval?

What Is Contour Interval?

It is the difference in elevation between two consecutive contour lines. For a contour map, the contour interval is always constant.


Factor affecting contour interval

Contour interval depends upon the following factor.

1. The Scale of The Map 

Contour interval is inverse proportion to the scale of the map. If the scale is small then the contour interval should be large and vice-versa.

2. Nature of The Ground

The general topography of the area decides the contour interval. For a flat area, the contour interval should be small. For sloping or undulating ground the contour interval is chosen should be large.

3. The Purpose And The Extent of the Survey Work

If the survey work is to be used for the accurate and detailed calculations, then the small contour interval is to be chosen and a large contour interval is chosen for the following cases:
  • For Catchment areas
  • For reservoir
  • For location survey
4. Time Available and Expense Admissible for the field and office work

Large contour interval is to be used if the time available for the survey work is less. The small contour interval, the survey work and plotting have to be more accurate. For small contour interval, the money required will also more as the field and office work will be more.

Consideration in making the choice of the proper contour interval

Before preparing a contour map, the contour interval required is decided. Considering the following factors on which contour interval depends
  • Nature of the ground surface
  • The scale of the Map
  • The purpose and extent of the survey
  • Time and expense required

The following contour intervals may be adopted for various purpose.
  1. Small scale maps or rough country              5m to 25 m
  2. Large scale maps pr flat country                  0.5 m
  3. Location survey                                            2 to 3 m
  4. Building sites                                                0.3 to 0.5 m
  5. Reservoir and town planning work               0.5 to 1 m
  6. Detailed design of works                              0.5 m
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Also, read - What is Contour?

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