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CONTOURS
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What are contours? Imaginary lines Drawn on a map Connecting places
Which are at equal elevation (height above sea level) How are contours drawn?
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S U R T Q E P G D F B M A C L I J H O K N
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238 240 252 276 263 297 279 280 300 317 320 285 325 314 289 309 298 280 254 281 264
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238 240 240 252 260 276 260 263 300 297 280 279 280 .300 317 320 285 325 314 320 289 309 300 298 280 280 280 254 281 260 264
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Contour Interval The difference of elevation between two successive contours Contour interval on the toposheet is 20 meters.
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INDEX CONTOURS Every 5th contour, with height mentioned
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Characteristics of Contours
All places on the contour line lie at the same elevation Contours never intersect each other Contour interval (difference between two successive contour values) is uniform throughout the map All contour values are multiples of the contour interval Height of any place on map can be determined
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Spacing between contours
Widely spaced contours Gentle slope Closely packed contours Steep slope Overlapping contours Vertical slope
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Let’s take a walk up a hill!
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We’re now at an elevation of 100 meters.
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Let’s keep going! 100m
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Now we’re at 200m. 200m 100m
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Shall we march on? 200m 100m
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We’ve made it to 300m! 300m 200m 100m
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On to the peak! 300m 200m 100m
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We’re on the peak, but what’s our elevation?
300m 200m 100m
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Let’s add contour lines for every 50 meters and see if that helps.
Any ideas? Let’s add contour lines for every 50 meters and see if that helps. 300m 200m 100m
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We know that we are above 350m, but less than 400m.
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Let’s head down the hill, it’s getting late!
350m 300m 250m 200m 150m 100m 50m
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Now what’s our elevation?
If you said somewhere between 200m and 250m you are right! 350m 300m 250m 200m 150m 100m 50m
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Let’s try this again! 350m 300m 250m 200m 150m 100m 50m
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What’s our elevation now?
If you said 50m or just under, you’re right! 350m 300m 250m 200m 150m 100m 50m
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Let’s now look at the same hill, but the way we might see it from an airplane!
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Each color change represents a 50 meter increase.
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Now, let’s try the same hike! Our elevation is 0 meters.
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Now what is our elevation?
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If you said more than 150 meters, but less than 200 meters your right!
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Let’s go a little higher.
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Think you know our elevation now?
More than 300meters But less than 350meters
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If we were standing on the peak, what would be our elevation?
More than 350 meters, less than 400 meters
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Let’s head down hill.
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Know our elevation?
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More than 100 meters, less than 150 meters
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FORM LINES Drawn where it is not possible to draw contours and there is a prominent relief feature which is lesser in height than the contour interval
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Types of slopes
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Uniform Gentle Slope
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Uniform Gentle Slope 320 280 300 260 240 220
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Uniform Steep Slope
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Uniform Steep Slope 260 320 300 180 200 220 240 140 160 280
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Concave Slope
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Concave Slope 240 220 320 260 280 300
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Convex Slope
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Convex Slope
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Features of Contour Diagrams
Spacing gives idea of slope Shape of contours resembles shape of relief feature in ariel view It is possible to visualise the shape of the relief feature
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VISUALISATION
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CONICAL HILL 320 300 280 260
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ASYMMETRICAL HILL 320 300 280 260
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CIRCULAR PLATEAU 320 300 280 260
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RIDGE 320 300 280 260
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SADDLE 320 300 280 260
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220 240 200 260 300 280
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V SHAPED VALLEY 320 340 300 280 260 240 220 200 180
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WATERFALL 320 340 300 280 260 240 220 200
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An Escarpment
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CONTOURS: 45 D/7 9293: Ridge 9289: Ridge (uniform) 9390: Ridge (steep) 9489: Hill 7975: Conical hill 9284: Conical hill 9782: Escarpment 9689: Saddle/ col 9783: Col/ Saddle 45 D/10 1907: Cliff( very steep) 2012: V shaped valley
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