Contouring MCQ Quiz - Objective Question with Answer for Contouring - Download Free PDF

Explanation:

Contour maps are used for:

i. Calculating the water capacity of reservoirs.

ii. Determining the catchment area of the drainage basin

• Contours are the most accurate method of representing relief features.
• Contouring is an act of using contour lines when representing the relief of an area on the map.
• Contour lines are the lines drawn on the map connecting all points on the earth’s surface with equal elevations above a fixed datum line (usually the mean sea level).
  • They are numbered in either feet or meters, above sea level. Usually, these numbers represent the exact elevation of land above sea level for all points along that line.
  • Contour lines never cross or intersect each other.
  • The spacing or gap between the contour lines represents the degree of slope.
  • Contour lines lie perpendicular to streams and rivers.

Some of the salient uses of contours are described below

1. Nature of Ground

2. To Locate Route

3. Intervisibility between Stations

4. To Determine Catchment Area or Drainage Area

5. Storage capacity of a Reservoir

Explanation:

True: Contour lines represent the intersection of a plane of a known elevation with the ground surface. Therefore, the contour line would pass through any point perpendicular to the line of the steepest slope at that point.

True: Contour lines represent distinct elevation values. Except in the case of overhanging cliffs or caves, they cannot intersect each other because no point on the ground can have two different elevations.

True: In the case of a vertical cliff, contour lines of different elevations could seem to unite and form a single line in some representations, indicating a sudden change in elevation.

False: Contour lines are not parallel to the watershed lines or ridgelines. Watersheds or ridgelines are traces of the points of the highest local elevations, while contour lines represent lines of constant elevation. The contour line can cross the watershed line but is not parallel to it.

Explanation:

Saddle Line:

• A saddle is the lowest area between two highlands (prominences or peaks) which has two wings that span the divide (the line between the two prominences) by crossing the divide at an angle, and, so is concurrently the local highpoint of the land surface which falls off in the lower direction
• A saddle is a low point between two areas of the higher ground. A saddle is illustrated by contour lines that typically look like an hourglass. Depression: A depression is a low point on the ground. It could be described as simply a hole in the ground that isn't a lake.

Explanation:

Analysis of the Given Statements

Statement 1 (S1): "The contour interval should be directly proportional to the scale to which it is proposed to draw the map."

Analysis:

• The scale of a map defines the ratio between distances on the map and actual ground distances.

• Large-scale maps (e.g., 1:10,000) cover smaller areas with high detail, meaning they require small contour intervals to capture finer terrain features.

• Small-scale maps (e.g., 1:250,000) cover large areas with low detail, so they require larger contour intervals to avoid excessive contour lines.

• Since S1 states that contour intervals are directly proportional to scale, this is incorrect. In reality, they are inversely proportional.

Conclusion: S1 is false.

Statement 2 (S2): "On a very flat terrain, smaller interval and on a hilly terrain, larger interval is adopted as the contour interval."

Analysis:

• In flat terrain, the elevation changes are gradual and small. If a large contour interval is used, the map may fail to show minor undulations in the ground. Therefore, a small contour interval is necessary for accurate representation.

• In hilly or mountainous terrain, elevation changes are steep and frequent. Using a small contour interval would result in too many contour lines, making the map cluttered and unreadable. Thus, a larger contour interval is used to maintain clarity while still showing important topographic features.

• This practice follows standard topographic mapping guidelines.

Conclusion: S2 is true.

Contours:

• Contours are imaginary lines on the surface of the earth, connecting points of equal elevation. They are used in topographic maps to represent the 3-dimensional terrain on a 2-dimensional surface.

Characteristics of Contour Lines:

• Permanent Structures: Contour lines do not pass through permanent structures such as buildings. This is because contours represent the natural terrain, and permanent structures are considered obstructions that modify the natural ground.
• Non-Crossing Contours: Contours of different elevations cannot cross each other. This is because each contour represents a distinct elevation level. However, there are exceptions like caves and overhanging cliffs where contours can appear to cross due to the vertical displacement.
• Closure of Contour Lines: A contour line must close upon itself, though not necessarily within the limits of the map. This means that contours form continuous loops, and even if they extend beyond the map boundaries, they will eventually close in on themselves.

The correct option is 2 (i, ii, and iii) because all the given statements accurately describe the characteristics of contour lines.

The different types of area measuring devices are as follows:

1. Clinometer or Inclinometer: It is used to measure angles of slopes either elevation or depression of an object with respect to gravity direction as reference.

2. Planimeter: It is the mechanical device used to measure area of plane. This measurement consists of dragging along boundary region.

Concept:

Contour Interval = 25/(No. of cm per km) (metres)

Also Contour Interval = 50/(No. of inches per mile) (feet)

Calculation:

For the scale of 1: 10000.

1 cm represents 10000 cm

∴ 1 cm represents 10000 × 10-5 km = 0.1 km

∴ 1 cm represents 0.1 km. So 1 km represent 10 cm

∴ Contour interval = 25/10 = 2.5 meters

Hence, the most appropriate answer is option 1.

Explanation:

Indirect Method of Contouring:

• Indirect methods are quicker, cheaper, and less laborious than the direct method
• In this method, a series of guide points are selected along with a system of straight lines and their elevations are determined
• These points are then plotted, and contours are drawn by interpolation

Three methods used for interpolation are as follows:

(i) By Estimation:

This is a rough method and is used on a small-scale map.

(ii) By Arithmetic Calculations

This is a very accurate method but a tedious one. The position of contours points between guide points is located by arithmetic calculations.

(iii) By Graphical Method

This is a rapid and convenient method and gives higher accuracy than the estimation method. It involves a lot of interpolation work.

Important points:

Arithmetical Calculation is considered more accurate than a graphical method, as the graphical method assumes only linear variation between the two guide points.

The geometric method is not used for interpolation of contours.

Explanation:

Horizontal Equivalent: 

(i) The horizontal distance between two points on two consecutive contour lines for a given slope is known as horizontal equivalent.

(ii) For a given contour interval, scale of the map and the nature of terrain decide the horizontal equivalent. As the slope becomes more and more steeper, the horizontal equivalent decreases.

Additional Information

Contour elevation:

(i) It is the line joining points of equal elevation on the surface of the earth.

Contour Interval: 

(i) The difference in elevation between successive contour lines on a given map is fixed. This vertical distance between any two contour lines on a map is called the contour interval.

Explanation:

Different characteristics of contours are as follows:

From the above observation:

Explanation:

Different methods of contouring are:

Tachometric method of contouring

• This method is used for angular surveying.
• This method is best suited for hilly terrains as the number of stations which can be commanded by a tachometer is far more than those by a level and thus the number of instrument settings is considerably reduced.

Direct Method

• The reduced level of different selected points is located and joined to form a contour.
• This method is accurate but very tedious and slow.

Square method or grid method

• In this method, we draw a grid point on the ground and measure the reduce level of all these points.
• It is generally used in plain terrain.

Cross Section method

• This method is generally used for hilly terrain to produce contour lines.

Explanation:

Contour is defined as an imaginary line on the ground surface joining the points of equal elevation.

Contours show distinct characteristic features of the terrain as follows:

1. Contour lines cross a watershed or ridgeline at right angles
2. No two contour lines can meet or cross each other except in the rare case of an overhanging or vertical cliff or wall
3. The direction of the steepest slope is along with the shortest distance between the contours.
4. In the direct method of contouring, the contours are not interpolated.
5. Closely spaced contour lines indicate a steep slope.
6. Widely spaced contour lines indicate a gentle slope.
7. Equally spaced contour lines indicate a uniform slope.
8. Closed contour lines with higher elevation towards the center indicate hills.
9. Closed contour lines with reducing levels towards the center indicate pond or other depression.
10. Contour lines of ridge show higher elevation within the loop of the contours. Contour lines cross the ridge at right angles.
11. Contour lines of the valley show reducing elevation within the loop of the contours. Contour lines cross the valley at right angles.
12. All contour lines must close either within the map boundary or outside.
13. All points on a contour line are of the same elevation.

Contour lines are the lines joining the points of equal elevation on the ground surface.

Characteristics of the contour lines are:

1. Two contour lines of different elevation cannot cross each other.

2. Contour lines of different elevations can unite to form one line only in case of a vertical cliff.

3. Contours lines crosses a valley or ridge line at 90°.

Concept:

Contour Map:

• From a contour map, the nature of the ground surface of an area can be known. So for identifying a suitable site for a dam or reservoir and for marking the tentative alignment of engineering projects involving roads, railways, etc. a contour map is essential.
• The horizontal scale is used to plot a contour map.

Contouring:

• Contours are the most accurate method of representing relief features.
• Contouring is the act of using contour lines when representing the relief of an area on the map.
• Contour lines are the lines drawn on the map connecting all points on the earth’s surface with equal elevations above a fixed datum line (usually the mean sea level).
  • They are numbered in either feet or meters, above sea level. Usually, these numbers represent the exact elevation of land above sea level for all points along that line.
  • Contour lines never cross or intersect each other.
  • The spacing or gap between the contour lines represents the degree of slope.
  • Contour lines lie perpendicular to streams and rivers.

Some of the salient uses of contours are described below

1. Nature of Ground

2. To Locate Route

3. Intervisibility between Stations

4. To Determine Catchment Area or Drainage Area

5. Storage capacity of a Reservoir

Explanation:

Depression:

A set of close contours with lower figures inside and higher figures outside indicates depression.

Given data:

The values from point A to point B are 500 m, 400 m, 300 m, 200 m, 200 m, 300 m, 400 m, and 500 m.

Additional Information

Hill: 

• A set of close contours with higher figures inside and lower figures outside indicates a hill.

Cliff:

• Cliffs are the steep rock faces along the sea coast and may be vertical where the contour line coincide with each other, an overhanging cliff where the contour lines intersect each other.