A contour is an imaginary line on the ground which connects the points have equal elevation.Contour is an important measurement for topographic maps.In this article we gonna teach you about contour map preparation.
A topographic map is a map which has the vertical and horizontal measurements of a plot.Topographic maps make a plan highly enhanced.A topographic map presets a clear picture of the surface of the ground.
By analyzing the contour elevation we can determine the shape of the ground.If the scale of a map is big, it shows nearly level surface, where it sloping or steel or gradual and if the scale is small, it shows hilly areas, valleys etc…
In the below section, we have mentioned about contour interval, characteristics of contours and uses of contour maps.Please head up through it.
- What are traverse surveying and its types?
- What is the permanent and temporary adjustment of theodolite?
Contour interval is the vertical distance between any consecutive contour is called contour interval.The contour interval is constant for a contour plan.
The horizontal distance between two contour lines is called horizontal equivalent.The horizontal equivalent depends upon the steepness of the ground.
The contour interval depends upon
- The nature of the ground
- The scale of the map
- The purpose of a survey
- The extent of survey
- Time of the survey
- The expense of field and office work
Characteristics of Contours
- Contour lines of different elevations can unite to form one line in case of a vertical cliff.
- Contour lines of different elevations cannot cross each other.However, contour lines of different elevation intersect only in case of an overhanging cliff.
- Contour lines close together indicates a steep slope.
- A contour passing through any point is perpendicular to the line of the steepest slope at that point.
- A closed interval with one or more contour lines lower one indicates a depression region.
- A closed interval with one or more higher ones inside it represents a hilly region.
- If the map is not within the limits, the contour lines must close itself.
- The last characteristics of the contour are contour lines cross a valley line right angle.
Contour gradient is a line lying throughout on the surface of the ground and preserving a constant inclination to the horizontal.
Use of contour maps
- Determination of intervisibility between two points.
- Drawing of sections.
- Measurement of drainage area is another use of contour maps
- Measurement of earthwork.
- Calculation of reservoir capacity.
- Error and Accuracy in Survey-Types of Error
- Levelling in Surveying-Objectives and methods of levelling
Below video shows, how to draw a contour map?