Latitude, Longitude and Time, Class 11 Practical Work in Geography

What Latitude, Longitude and Time is about

Key concepts

Shape of the earth and the geographical grid

NCERT section Latitude, Longitude and Time (introduction)

• The earth is nearly a sphere: the equatorial and polar radii differ because rotation causes bulging at the equator; the shape resembles an oblate spheroid.
• On such a surface there is no natural reference point, so we draw a network of imaginary lines on globes and maps.
• The earth spins west to east on its axis, giving two natural reference points: the North and South Poles.
• The geographical grid is a network of intersecting lines: horizontal parallels of latitude and vertical meridians of longitude.
• Latitude and longitude are geographical coordinates: with them we can find location, distance and direction of points.
• Only selected lines are drawn on a map, though infinitely many are possible.
• Units: degrees (°), each of 60 minutes ('), each of 60 seconds ("), because they are angular distances.

Worked example

Why do we need a geographical grid to locate places on the earth? (2 marks)

Try it first, then show the solutionSolution

1. The earth is nearly a sphere (an oblate spheroid), so its surface has no natural point from which to measure other positions.
2. A grid of parallels and meridians, based on the two poles, gives coordinates (latitude and longitude) that fix any place exactly.

Answer: A curved surface has no natural reference point; the grid supplies coordinates.

Parallels of latitude

NCERT section Parallels of Latitudes

Definition: the latitude of a place is its distance north or south of the equator, measured along its meridian as an angle from the centre of the earth. Lines joining places of equal latitude are parallels.

Key facts:

• Equator (0°): drawn midway between the poles; the largest circle; divides the globe into two equal halves: a great circle.
• Other parallels get smaller towards the poles and divide the earth into unequal parts: small circles.
• Poles: 90°N and 90°S. Write N or S with the value.
• At 1° intervals: 89 parallels in each hemisphere, 179 in all including the equator.
• Length of 1° of latitude: about 111 km if the earth were a perfect sphere; in fact it changes slightly from 110.6 km at the equator to 111.7 km at the poles.
• Latitude can be found from the altitude of the sun or the Pole Star.
• Latitudes demarcate temperature zones: 0°-23½° torrid, 23½°-66½° temperate, 66½°-90° frigid (both hemispheres).

Worked example

Two places lie on the same meridian at 10°N and 25°N. Estimate the distance between them. (2 marks)

Try it first, then show the solutionSolution

1. Difference in latitude = 25° - 10° = 15°.
2. 1° of latitude ≈ 111 km, so distance ≈ 15 × 111 = 1,665 km.

Answer: About 1,665 km.

Meridians of longitude

NCERT section Meridians of Longitude

Definition: a place's longitude is the angle, in degrees, by which it lies east or west of the Prime Meridian.

Key facts:

• Meridians are semicircles converging at the poles; two opposite meridians together make a circle but are valued separately.
• They cross the equator at right angles and are all equal in length.
• The meridian through the Greenwich observatory (near London) is the Prime Meridian (0°) by international agreement.
• Values run 0° to 180° east and west; the part east of the Prime Meridian is the eastern hemisphere, west of it the western hemisphere.
• Spacing between meridians is greatest at the equator (111.3 km), 79 km at 45°, 0 km at the poles.

Comparison (Table 3.1):

Parallels of latitude	Meridians of longitude
Angular distance N or S of the equator	Angular distance E or W of Greenwich, 0°-180°
All parallel to the equator	All converge at the poles
Appear as circles on a globe	Appear as circles through the poles (semicircles each)
About 111 km apart	111.3 km at equator → 79 km at 45° → 0 at poles
0° = equator, 90° = poles	360° in all, 180° E and 180° W
Mark temperature zones	Used to find local time from the Prime Meridian

Worked example

Why is the distance between two meridians 79 km at 45° but 111.3 km at the equator? (2 marks)

Try it first, then show the solutionSolution

1. Meridians are farthest apart at the equator and converge to a point at each pole.
2. So the gap between two meridians shrinks with latitude: 111.3 km at 0°, 79 km at 45°, 0 at 90°.

Answer: Meridians converge towards the poles.

Drawing parallels and meridians

NCERT section Drawing the Parallels of Latitudes; Meridians of Longitude

Drawing a parallel (e.g. 20°S) (Figure 3.2):
1. Draw a circle; draw a horizontal line through its centre for the equator.
2. Place a protractor with its 0°-180° line on the equator.
3. For 20°S, mark 20° below the equator on both east and west sides; the arms cut the circle at two points.
4. Join the two points with a line parallel to the equator: that is 20°S.

Drawing meridians (view from above the North Pole) (Figures 3.4, 3.5):
1. Draw a circle; its centre is the North Pole, its circumference the equator.
2. Draw a vertical line through the centre: the 0° and 180° meridians, meeting at the pole.
3. Imagine standing at the North Pole: east and west reverse: east is on your left, west on your right.
4. Place the protractor along the 0°-180° line and measure 45° on both sides: 45°E on the left, 45°W on the right.

Worked example

When drawing meridians on a polar view centred on the North Pole, why is 45°E marked on the left? (2 marks)

Try it first, then show the solutionSolution

1. On an ordinary map east is to the right, but in a polar view you imagine looking down from above the North Pole.
2. From that position east and west reverse, so east lies to your left and 45°E is drawn on the left of the 0° line.

Answer: Viewed from above the North Pole, east appears on the left.

Longitude and time

NCERT section Longitude and Time

Basis: the earth rotates west to east, making the sun appear to rise in the east and set in the west. One rotation = 360° in 24 hours, so:

• 15° of longitude per hour
• 1° of longitude every 4 minutes

Rule (from NCERT's worked examples):

• Places east of a meridian are ahead in time (add 4 minutes per degree).
• Places west are behind (subtract 4 minutes per degree).

NCERT examples: Thimphu (90°E) when Greenwich is 12 noon: 90 × 4 = 360 min = 6 h ahead → 6 pm. New Orleans (90°W): 6 h behind → 6 am.

Steps for any problem:
1. Find the longitude difference (subtract if same side of 0°, add if on opposite sides).
2. Multiply by 4 minutes; convert to hours and minutes.
3. Add if the place is east, subtract if west.
4. Adjust past midnight or noon (and the date if needed).

Worked example

When it is 2:00 pm at a place on 30°E, what is the local time at a place on 60°W? (3 marks)

Try it first, then show the solutionSolution

1. The places lie on opposite sides of the Prime Meridian: difference = 30 + 60 = 90°.
2. Time difference = 90 × 4 = 360 minutes = 6 hours.
3. 60°W is west of 30°E, so it is behind: 2:00 pm - 6 h = 8:00 am.

Answer: 8:00 am.

Standard time, time zones and the International Date Line

NCERT section International Date Line

Standard time: to keep one time within a country, the local time of a central (standard) meridian is used for the whole country. It is chosen in multiples of 7°30' (divisible by 15° or 7°30'), so the difference from GMT is a whole number of hours or half-hours.

IST: based on 82°30'E, passing through Mirzapur: 82.5 × 4 = 330 minutes, so IST = GMT + 5 h 30 min.

Several zones: countries with large east-west spans, such as Russia, Canada and the USA, use more than one standard meridian. The world is divided into 24 major time zones (Figure 3.6).

International Date Line (IDL):

• There must be a place where the date changes. The IDL runs approximately along 180°.
• Time at 180° is 12 hours from 0°: going east it is 12 h ahead, going west 12 h behind, so the two sides differ by a whole day.
• Crossing the IDL eastward, a traveller counts the day one day back (NCERT: Tuesday becomes Monday); crossing westward, one day forward (Tuesday becomes Wednesday).

Worked example

A ship crosses the International Date Line travelling east on a Friday. What day will the crew count after crossing, and why? (2 marks)

Try it first, then show the solutionSolution

1. Travelling east from the Prime Meridian, time runs ahead until it is 12 h ahead at 180°; just across the line it is 12 h behind.
2. So crossing eastward the date goes back one day: Friday becomes Thursday (as NCERT's Tuesday becomes Monday).

Answer: Thursday: crossing eastward sets the calendar back a day.

Latitude, Longitude and Time in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Topics in this chapter

• The Geographical Grid: Parallels of Latitude, Meridians of Longitude and How to Draw Them
• Longitude and Time: Local Time, Standard Time, Time Zones and the International Date Line

Latitude, Longitude and Time: key facts

Angular units

$1°=60^{\prime };1^{\prime }=60"$

Latitude and longitude are angles.

Rotation rate

$360°/24h=15°perhour=1°per4minutes$

Basis of all time sums.

Local time

$Localtime=knowntime\pm (longitudedifference\times 4min);+ifeast,-ifwest$

Opposite hemispheres: add longitudes to get the difference.

Longitude from time

$Longitudedifference=timedifference(min)÷4$

2 h 40 min ahead of GMT → 40°E.

IST

$82°30^{\prime }E\times 4min=330min\to GMT+5h30min$

Standard meridians in multiples of 7°30'.

Parallels count

$At1°interval:89+89+equator=179$

Poles are points, not lines.

Degree lengths

$1°latitude\approx 111km(110.6equator,111.7poles);1°longitude:111.3km(0°),79km(45°),0km(90°)$

Meridians converge.

Temperature zones

$Torrid0°-23½°;temperate23½°-66½°;frigid66½°-90°$

Both hemispheres.

Date Line

$Crossing180°eastward:date-1;westward:date+1$

24 time zones in the world.

Latitude, Longitude and Time: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

Tricks to remember Latitude, Longitude and Time

Short memory aids. Say each one aloud once, then use it on a question the same day.

• Time rule

  'East Early, Add; West Waits, Subtract'.

  Use it when: Local time sums.

• Four minutes

  '1 degree = 4 minutes; 15 degrees = 1 hour'.

  Use it when: All time questions.

• IST

  '82 and a half, 5 and a half'.

  Use it when: IST questions.

• Date Line

  'Go East, lose a day (Tuesday → Monday); go West, gain a day (Tuesday → Wednesday)'.

  Use it when: IDL questions.

Where students lose marks in Latitude, Longitude and Time

The slips examiners see most often, and what to write instead.

• ✗Mistake: Subtracting time for places east

  Direction rule reversed (NCERT's own wording in one line is confusing).

  Wrong working

  Noon at Greenwich → 2:00 am at 150°E.

  Right working

  East is ahead: 150 × 4 = 600 min = 10 h → 10:00 pm.

  ✓Do this: East is early to see the sun, so its clocks are ahead: add for east.

  Usually costs: Full marks for the sum.

• ✗Mistake: Subtracting longitudes on opposite sides of 0°

  Treating E and W as the same side.

  Wrong working

  30°E and 60°W differ by 30°.

  Right working

  Opposite sides: 30 + 60 = 90°.

  ✓Do this: Same side subtract, opposite sides add.

  Usually costs: Full marks for the sum.

• ✗Mistake: Counting 180 parallels

  Forgetting the equator is counted once and poles are points.

  Wrong working

  There are 180 parallels at 1° interval.

  Right working

  89 in each hemisphere plus the equator = 179.

  ✓Do this: Poles are points.

  Usually costs: Marks in an MCQ or viva.

• ✗Mistake: Marking 45°E on the right in a polar view

  Habit from ordinary maps.

  Wrong working

  45°E drawn to the right of the 0° line.

  Right working

  Viewed from above the North Pole, 45°E is on the left.

  ✓Do this: Stand at the pole: east flips left.

  Usually costs: Marks in construction.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.What shape does the earth resemble?Show answer

   An oblate spheroid (nearly a sphere, bulging at the equator).

2. 2.What gives the earth its two natural reference points, and what are they?Show answer

   Its west-to-east rotation on its axis; the North and South Poles.

3. 3.Which is the only parallel of latitude that is a great circle?Show answer

   The equator: it divides the globe into two equal halves; all other parallels are small circles.

4. 4.How long is one degree of longitude at 45°?Show answer

   About 79 km.

5. 5.Through which town does India's standard meridian pass?Show answer

   Mirzapur.

6. 6.How many major time zones does the world have?Show answer

   24.

7. 7.Why does a town at 88°E see sunrise before a town at 77°E on the same day?Show answer

   The earth rotates west to east, so places farther east face the sun first: 11° × 4 = 44 minutes earlier.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Practical exam chapter: 4 marks.
• ☐Earth: oblate spheroid; poles are the natural reference points.
• ☐Latitude: N/S of the equator, 0°-90°; 179 parallels at 1°; 1° ≈ 111 km.
• ☐Longitude: E/W of Greenwich, 0°-180°; meridians equal semicircles; gap 111.3 km (0°) → 79 km (45°) → 0 (poles).
• ☐360° in 24 h: 15° per hour, 1° per 4 min; east ahead, west behind.
• ☐Thimphu 90°E at GMT noon = 6 pm; New Orleans 90°W = 6 am.
• ☐Standard meridians in multiples of 7°30'; IST 82°30'E (Mirzapur) = GMT + 5:30.
• ☐24 time zones; IDL about 180°: eastward crossing → date back one day, westward → forward one day.

Latitude, Longitude and Time: frequently asked questions