How To Find The Contour Interval Of A Map

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Contents:

What is Contour Interval?
Factors Affecting the Selection of Profile Interval
How to Calculate Contour Interval from Maps?
- Stride 1:
- Pace 2:
- Footstep 3:
- Pace 4:
- Step 5:
- Step half-dozen:
- Case Calculation of Profile Intervals:
Uses of Contour Intervals in Surveying

What is Contour Interval?

A contour interval in surveying is the vertical distance or the difference in the elevation between the two contour lines in a topographical map. Usually there are different profile intervals for the unlike maps. Because the size of the area to be mapped, profile intervals are assumed. In every map, on the right-hand bottom side, the contour interval is specified. When the contour interval is non specified in the map, information technology can be calculated every bit explained in the following sections. The unremarkably used contour interval is xx feet for a 1:24,000 map scale.

Factors Affecting the Selection of Contour Interval

The option of the profile interval is decided by the survey leader before the starting time of the mapping process depending upon the ground factors.

Sl. No	Factors	Select High CI like 1m, 2m, 5m or more	Select Low CI like 0.5m, 0.25m, 0.1m or less
i	Calibration of the map	For small calibration maps covering a wide area of varying terrain	For large maps showing details of a small area
2	Extent of survey	For rough topographical map meant for initial cess simply	If a detailed map is to exist prepared for execution work
3	Nature of ground	If the footing has big variation in levels, for instance, hills and ponds	If the terrain is comparatively level
4	Time and resources available	If less fourth dimension and resources are available	If time and resources abundant

How to Calculate Contour Interval from Maps?

A contour map consists of contour lines of a given geographical region. To continue the profile map simple and easy to read, not every contour line is marked with its pinnacle reading. These marked or labeled lines are known or termed as Index Contour Lines. In the above figure, the dark lines with reading are alphabetize contour lines. The adding of the profile intervals is every bit beneath:

Pace ane:

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

Step 2:

At present calculate the difference betwixt the two-selected index contour line selected from a map. To take the deviation, subtract the higher elevated line with the lower elevated line reading.

Step iii:

Now count the number of non-index lines contour lines between the ii index contour lines selected for the profile interval calculating in the 1^st step.

Stride 4:

The number of lines obtained in the in a higher place step is taken and added with 1. For Ex: If the number of lines between 2 index lines are 5. Then add 1 to five that becomes 6.

Footstep v:

the terminal step is the quotient of the deviation between 2 index lines (step 2) and the number of lines in between two index lines plus 1 (step 5).

Step 6:

The terminal answer we go after dividing is the contour interval of the specific topographical map

Example Adding of Contour Intervals:

Considering the above map, the steps involved in contour interval calculation are, Permit's assume, 7000 and 7100 and summate the interval between information technology. Now difference between 7100 and 7000 is 7100 - 7000 = 100 The number of contour lines in-between 7000 and 7100 are four. Adding 1 to 4, iv + i = 5 Now dividing 100 by 5, 100/5 = 20 units The Contour Interval of the in a higher place map united states 20 Units.

Uses of Contour Intervals in Surveying

When a large area is to be mapped in small piece of paper contour intervals are used. A higher profile interval is used for a large area and small contour interval for small area.
In a large map, index contour lines are less to continue it simple to read the map easily. In this instance, to observe out the intermediate points summit, contour intervals are used.
Earthwork estimations for whatsoever type of structure similar bridges, dams or roads tin can be found out with the help of profile intervals in a map.

As contour intervals are for the calculation of vertical pinnacle of an surface area, same style to calculate the horizontal distance it is termed every bit Horizontal Equivalent. The horizontal distance between two points on two consecutive contour lines for a given slope is known every bit horizontal equivalent. The difference between Contour intervals and Horizontal Equivalent are tabulated below:

S. No	Contour 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 actual distance by multiplying with the scale of the map
3	In a given map the contour interval is a constant	The horizontal equivalent varies with slope. Closer distance indicates steep slope and wider distance gentle slope