In cartography, contour lines are an imaginary line of a terrain that joins the point of equal elevation above a given level, such as mean sea level or benchmark.
Characteristics of Contour Lines in Surveying
Following are the characteristics of contour lines in surveying for reading contour maps:
- No two lines meet on intersect each other in any case.
- All lines close themselves within the map boundaries or outside it.
- If the contour lines are very close to each other, this indicates steep slope.
- If the contour lines are at very large distance to each other, this indicates a gentle slope.
- If the closed lines have higher elevation in the center then it represents the hill or mountain.
- If the closed line have increasing elevation as we move away, then it represents a pond or a depression in the ground profile.
- In a single contour line, at any point the elevation is same.
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Types of Contour Lines in Surveying and their Importance
Contour lines are differentiated into many types based upon the function it denotes, they are listed as below:
- Isopleth
- Isohyet
- Isobar
- Isobath
- Isohaline
- Isotherm
- Isohel
- Isohume
- Isoneph
- Isopectic
- Isotach
- Isogeotherm
Following are the uses and importance of different types of contour lines in surveying:
1. Isopleth
Isopleth on a contour map connects the places having the same value of some measurable quantity of geographical or meteorological phenomena.
For Ex. The population density of an area can be calculated by the quotient of population in the area and surface area of a region.
2. Isohyet
Isohyet indicates the points of equal rainfall of an area in the given time.
3. Isobar
Isobars on contour maps indicates the point of equal or constant atmospheric pressure for a given period.
This type of contour is used in the prediction of future weather patterns isobars are commonly used in television weather reporting.
4. Isobath
It is a type of imaginary contour lines on a map of chart that connects all the points having same depth below water surface like ocean, sea and lake.
5. Isohaline
It is a type of contour lines on a map which connect the point of equal salinity in the water body (majorly contour).
6. Isotherm
It is a type of contour lines on a map of chart with connects the point of equal temperature of a given area.
Further they are divided into two types.
- Isocheim: It is a line of equal mean winter temperature.
- Isothere: It is a line of equal means summer temperature.
An isotherm at 0 degree is called freezing level.
7. Isohel
It is a type of contour lines on a map that connects the places of equal duration of sunshine for a given period.
8. Isohume
It is a type of contour lines on a map that connects all the points of equal relative humidity of a specific area.
9. Isoneph
It’s a line that connects all points of equal amount of cloud cover.
10. Isopectic
Isopectic is imaginary lines on a contour map or chart that connects all the points at which the ice starts to form at the same time.
11. Isotach
It’s a line that connects all points of equal wind speed.
12. Isogeotherm
Isogeotherm on contour map connects all the points within the earth having the same mean temperature.
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