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10. 9. 8. 7. 6. 5. 4. 3. 2. 1. C ONTOURS. What are contours?. Imaginary lines Drawn on a map Connecting places Which are at equal elevation (height above sea level). How are contours drawn?. S. U. R. T. Q. E. P. G. D. F. B. M. A. C. L. I. J. H. O. K. N. 238.

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C ONTOURS

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CONTOURS


What are contours?

  • Imaginary lines

  • Drawn on a map

  • Connecting places

  • Which are at equal elevation (height above sea level)

How are contours drawn?


S

U

R

T

Q

E

P

G

D

F

B

M

A

C

L

I

J

H

O

K

N


238

240

252

276

263

297

279

280

300

317

320

285

325

314

289

309

298

280

254

281

264


238

240

240

252

276

260

260

263

280

297

300

279

280

.300

317

320

285

325

314

320

289

309

300

298

280

280

280

254

281

260

264


Contour Interval

  • The difference of elevation between two successive contours

  • Contour interval on the toposheet is 20 meters.


INDEX CONTOURS

Every 5th contour, with height mentioned


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


Spacing between contours

  • Widely spaced contours

    • Gentle slope

  • Closely packed contours

    • Steep slope

  • Overlapping contours

    • Vertical slope


Let’s take a walk up a hill!


We’re now at an elevation of 100 meters.

100m


Let’s keep going!

100m


Now we’re at 200m.

200m

100m


Shall we march on?

200m

100m


We’ve made it to 300m!

300m

200m

100m


On to the peak!

300m

200m

100m


We’re on the peak, but what’s our elevation?

300m

200m

100m


Any ideas?

Let’sadd contour lines for every 50 meters and see if that helps.

300m

200m

100m


We know that we are above 350m, but less than 400m.

350m

300m

250m

200m

150m

100m

50m


Let’s head down the hill, it’s getting late!

350m

300m

250m

200m

150m

100m

50m


Now what’s our elevation?

If you said somewhere between 200m and 250m you are right!

350m

300m

250m

200m

150m

100m

50m


Let’s try this again!

350m

300m

250m

200m

150m

100m

50m


What’s our elevation now?

If you said 50m or just under, you’re right!

350m

300m

250m

200m

150m

100m

50m


Let’s now look at the same hill, but the way we might see it from an airplane!


Each color change represents a 50 meter increase.


Now, let’s try the same hike! Our elevation is 0 meters.


Now what is our elevation?


If you said more than 150 meters, but less than 200 meters your right!


Let’s go a little higher.


Think you know our elevation now?

More than 300meters

But less than 350meters


If we were standing on the peak, what would be our elevation?

  • More than 350 meters, less than 400 meters


Let’s head down hill.


Know our elevation?


More than 100 meters,

less than 150 meters


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


Types of slopes


Uniform Gentle Slope


Uniform Gentle Slope

320

280

240

260

300

220


Uniform Steep Slope


Uniform Steep Slope

320

260

300

240

220

200

180

280

160

140


Concave Slope


Concave Slope

240

220

320

260

280

300


Convex Slope


Convex Slope


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


VISUALISATION


320

300

280

260

CONICAL HILL


320

300

280

260

ASYMMETRICAL HILL


320

300

280

260

CIRCULAR PLATEAU


260

320

280

300

RIDGE


260

320

280

320

300

SADDLE


240

220

300

260

200

280


340

280

260

240

320

220

200

300

180

V SHAPED VALLEY


340

280

260

240

320

220

300

200

WATERFALL


An Escarpment


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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