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Contents:

  • What is Contour Interval?
  • Factors Affecting the Selection of Contour Interval
  • How to Calculate Profile Interval from Maps?
    • Pace 1:
    • Step two:
    • Step 3:
    • Step 4:
    • Step 5:
    • Step vi:
    • Instance Calculation of Contour Intervals:
  • Uses of Contour Intervals in Surveying

What is Contour Interval?

A profile interval in surveying is the vertical distance or the deviation in the elevation betwixt the ii contour lines in a topographical map. Usually there are different contour intervals for the different maps. Because the size of the area to be mapped, contour intervals are causeless. In every map, on the right-hand bottom side, the contour interval is specified. When the profile interval is not specified in the map, it tin be calculated every bit explained in the following sections. The commonly used contour interval is 20 feet for a 1:24,000 map calibration. What is Contour Interval? Its Calculation and Uses in Surveying

Factors Affecting the Option of Contour Interval

The selection of the profile interval is decided by the survey leader before the beginning of the mapping procedure depending upon the ground factors.

Sl. No Factors Select Loftier CI like 1m, 2m, 5m or more than Select Low CI like 0.5m, 0.25m, 0.1m or less
1 Scale of the map For small scale maps covering a broad area of varying terrain For large maps showing details of a modest area
2 Extent of survey For rough topographical map meant for initial assessment only If a detailed map is to exist prepared for execution work
3 Nature of ground If the basis has large variation in levels, for instance, hills and ponds If the terrain is insufficiently level
four Time and resources available If less fourth dimension and resources are available If time and resources arable

How to Calculate Contour Interval from Maps?

A contour map consists of contour lines of a given geographical region. To go along the contour map simple and easy to read, not every contour line is marked with its elevation reading. These marked or labeled lines are known or termed as Index Contour Lines. How to Calculate Contour Intervals from Maps? In the above effigy, the dark lines with reading are index contour lines. The calculation of the profile intervals is as below:

Pace 1:

Firstly locate 2 alphabetize contour lines that are labeled with a specific superlative.

Step ii:

Now calculate the divergence between the two-selected alphabetize contour line selected from a map. To have the difference, decrease the higher elevated line with the lower elevated line reading.

Step 3:

At present count the number of non-alphabetize lines contour lines betwixt the 2 index contour lines selected for the profile interval computing in the 1st stride.

Step 4:

The number of lines obtained in the above step is taken and added with 1. For Ex: If the number of lines between two index lines are 5. Then add 1 to 5 that becomes 6.

Step 5:

the final stride is the caliber of the difference between 2 index lines (pace 2) and the number of lines in between two index lines plus one (step 5).

Step 6:

The final answer we get subsequently dividing is the contour interval of the specific topographical map

Example Calculation of Profile Intervals:

Example Calculation of Contour Intervals Considering the above map, the steps involved in contour interval calculation are, Let'due south assume, 7000 and 7100 and calculate the interval betwixt it. Now deviation between 7100 and 7000 is 7100 - 7000 = 100 The number of contour lines in-between 7000 and 7100 are 4. Adding one to four, 4 + ane = 5 Now dividing 100 past v, 100/5 = 20 units The Profile Interval of the to a higher place map us 20 Units.

Uses of Contour Intervals in Surveying

  1. When a big expanse is to exist mapped in modest piece of paper contour intervals are used. A college contour interval is used for a large area and small contour interval for small surface area.
  2. In a large map, index contour lines are less to keep it uncomplicated to read the map easily. In this example, to observe out the intermediate points meridian, profile intervals are used.
  3. Earthwork estimations for whatever type of structure similar bridges, dams or roads tin exist found out with the aid of contour intervals in a map.

Every bit contour intervals are for the calculation of vertical elevation of an area, same way to calculate the horizontal distance it is termed equally Horizontal Equivalent. The horizontal distance between two points on two sequent contour lines for a given gradient is known every bit horizontal equivalent. The deviation between Contour intervals and Horizontal Equivalent are tabulated below:

Southward. No Profile Interval Horizontal Equivalent
1 It is based on vertical levels Represents horizontal distance
2 No measurement or scaling is required since the contour levels are indicated on the contour lines The distance must be measured on the map and converted to bodily distance by multiplying with the scale of the map
iii In a given map the contour interval is a abiding The horizontal equivalent varies with slope. Closer distance indicates steep slope and wider distance gentle slope

Read More: Profile Lines and Its Types, Characteristics and Uses in Surveying Contour Maps and Their Uses Methods of Contouring