Measurement or scaling is not required because contour levels are indicated on contour lines. The horizontal distance between two factors on two contour lines for a given slope is known as the horizontal equivalent. Difference between Contour interval & Horizontal equivalent: Contour interval Horizontal equivalent The contour interval is used to calculate the vertical elevation of a location. The contour interval of the above map gave us 20 units. The variety of contour lines is 4 between 70. ![]() Now the difference between 71 is 7100 – 7000 = 100. Let’s say, 70 and calculate the interval between them. Example contour interval calculation:Ĭonsidering the map, the following steps are used to calculate the contour intervals calculation as follows: The final answer is obtained by dividing the contour intervals of the particular topographic map. ![]() The ultimate step is the quotient of the difference between the index lines (step 2) and the variety of lines between the 2 index lines plus 1 (step 5). The variety of lines obtained within the above step is taken and added with 1.įor example: if the variety of rows between 2 index lines is 5, then add 1 to 5 which turns into 6. Now calculate the number of non-index lines contour lines between the two indexed contour lines chosen for the contour interval calculated in the 1st step. To take the difference, subtract the upper elevation line with lower elevation line. The calculation of the contour intervals is as follows:įirst, find the two index contour lines which can be labelled with a particular height.Ĭalculate the difference between the 2 selected index contour lines from a map. To maintain the contour map easy and simple to learn, every contour line is not marked by its elevation studying, these marked or labelled lines are identified or known as index contour lines. How to Calculate Contour Interval from Maps?Ī contour map consists of contour lines of a given geographic area. Time and resources available: If much less time and resources can be found. Nature of ground: If there’s a massive change in ground levels, for example, hills and ponds. If a detailed map is to be prepared for the execution work. Extent of the survey: For rough topographic map means for preliminary assessment only. For large maps showing details of a small area. Scale of the map: For small scale maps covering a large area of different areas. Select Low CI like 0.5m, 0.25m, 0.1m or less. Factors: Select High CI like 1m, 2m, 5m or more. The choice of the contour interval is determined by the survey leader before the beginning of the mapping process based on ground factors as follows. Factors Affecting the Selection of Contour Interval: When the contour interval is not specified within the map, it may be calculated within the following sections, the generally used contour interval is 20 feet for a 1: 24,000 map scale. There are 3 types of contour lines on a map.A contour interval is a vertical distance or a difference in elevation between contour lines in a topographic map, index contour lines are bold or thick lines that appear on every fifth contour line and if the number associated with specific contour lines is increasing, the elevation of the area is also increasing.įor the plotting of region, the contour intervals are assumed, the contour intervals is specified on the right-hand side. What are the different types of contour lines? To ascertain the profile of the ground surface in any direction.Ĥ. ![]() To find the economical route of communication between two places.Ĩ. We can find the difference in the height of any two points.ħ. The contour gradient can be drawn from the map.Ħ. We can calculate the area & capacity of a reservoir or any water bodies.ĥ. We can determine the area & volume of the earth of a particular locality.Ĥ. Helps to select the location of infrastructures such as dams, bridges, pipelines, roads, etc.ģ. Contour map provides the topography of the ground.Ģ. What are the uses of contour maps in surveying?ġ. For the rough survey work such as location survey, finding catchment area, finding the capacity of water bodies, etc. For the larger scale map, the contour intervals are made of less spacing.įor the precise & detailed survey work, the contour interval should be smaller. The contour spacing will be large for a map having a small scale. Steep slope: The contour intervals are generally big & are unequal Plain ground: The contour intervals are generally small & are parallel. The contour interval depends upon the following factors. What are the factors that affect the selection of contour intervals? For eg: Suppose a contour map has a contour line of 80, 85, 90, 95, & so on,Ģ.
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