C ONTOURS

CONTOURSCONTOURS

What are contours?

• Imaginary lines• Drawn on a map• Connecting places• Which are at equal elevation (height above

sea level) How are contours drawn?

How are contours drawn?

A

J

E

F D

C

B

T

P

H

L

S

O

R

N

Q

I

M

K

G

U

325

298

297

317 300

314

320

276

279

280

289

238

254

252

264

263

309

285

281

280

240

325

298

297

317 .300

314

320

276

279

280

289

238

254

252

264

263

309

285

281

280

240

320

240

260

280

300

280

280

260

260

300

Contour IntervalContour Interval

• The difference of elevation between two successive contours

• Contour interval on the toposheet is 20 meters.

INDEX CONTOURSEvery 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.

100m

200m

Shall we march on?

100m

200m

We’ve made it to 300m!

100m

200m

300m

On to the peak!

100m

200m

300m

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

100m

200m

300m

Any ideas?

100m

200m

300m

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

100m

200m

300m

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

50m

150m

250m

350m

100m

200m

300m

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

50m

150m

250m

350m

100m

200m

300m

Now what’s our elevation?

50m

150m

250m

350m

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

100m

200m

300m

Let’s try this again!

50m

150m

250m

350m

100m

200m

300m

What’s our elevation now?

50m

150m

250m

350m

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

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

320 300

280

260

240 220

Uniform Steep Slope

Uniform Steep Slope

320300280

260240220

200

180

160

140

Concave Slope

Concave Slope

320 300280

260240 220

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

CONICAL HILL

320

300

280

260

ASYMMETRICAL HILL

320300

280

260

CIRCULAR PLATEAU

320300280

260

RIDGE

320300

280 260

SADDLE

320300

280 260320

V SHAPED VALLEY

320

340

300

280260

240

220200

180

WATERFALL

320

340

300

280260

240

220

200

An Escarpment

CONTOURS: 45 D/7 9293: Ridge9289: Ridge (uniform)9390: Ridge (steep)9489: Hill7975: Conical hill9284: Conical hill9782: Escarpment9689: Saddle/ col9783: Col/ Saddle

45 D/101907: Cliff( very steep)2012: V shaped valley