Geographic Grid: Latitudes and Longitudes

Latitude, Longitude

Reason — Lines of latitude (parallels) run horizontally from east to west around the globe, measuring distances north or south of the Equator. Lines of longitude (meridians) run vertically from north to south, meeting at the poles and measuring distances east or west of the Prime Meridian.

Geographic Grid

Reason — Lines of latitude and longitude intersect to form a criss-crossing network on a map or globe known as the Geographic Grid. This framework is essential for pinpointing the exact coordinates and location of any place on the Earth's surface.

All of the above

Reason — Lines of latitude are imaginary, parallel circles drawn on the globe that run east to west. Unlike lines of longitude, they are not equal in length; they are largest at the Equator and shrink progressively as they move toward the poles, where they become mere points (90°N and 90°S).

60°

Reason — The lines of latitude are not of equal length and become smaller as we move towards the poles. At 60° latitude, in each hemisphere, the length of the circle is exactly half the length of the Equator.

181

Reason — Parallels of latitude are drawn at 1° intervals from the Equator (0°) to the poles (90°). This creates 90 parallels in the Northern Hemisphere and 90 in the Southern Hemisphere, totalling 181 parallels when including the Equator.

90°

Reason — The Equator is marked as 0° latitude. The North Pole and the South Pole lie opposite to each other at the extreme ends of the earth, each located at an angular distance of 90° north and 90° south of the Equator respectively.

Torrid Zone : 23 1/2 °N to 23 1/2 °S

Reason — The Torrid Zone is correctly defined as the region extending between the Tropic of Cancer (23 1/2°N) and the Tropic of Capricorn (23 1/2°S). In contrast, the Temperate Zones lie between the Tropics and the Polar Circles (23 1/2° to 66 1/2°), while the Frigid Zones are located between the Polar Circles and the Poles (66 1/2° to 90°).

They are 360 lines at 1° interval.

Reason — Lines of longitude are drawn around the globe at 1° intervals, totalling 360 lines. Unlike parallels of latitude, they do not run parallel to each other; instead, they are individual semicircles that converge at the North and South Poles.

(a) 40°

Reason — Longitude is the angular distance of a place east or west of the Prime Meridian, measured at the centre of the earth. Since OA lies along the Prime Meridian (0°) and OB lies along the 40° Meridian, the angle AOB at the centre of the earth is equal to 40°.

(b) Great circle

Reason — The Equator is the only line of latitude that passes through the centre of the earth and divides it into two equal halves. As the circle passing through E and Q represents the Equator, it is a Great Circle.

(c) =

Reason — All meridians of longitude converge at the poles and are of equal length. Therefore the length of the Prime Meridian is equal to (=) the length of the 40° Meridian.

Both A and R are true but R does not explain A.

Explanation — The length of the Equator is equal to the circumference of the earth or 40,075 km. Since the circumference of a circle is equal to 360°, the 1° angular distance is roughly equal to 111 km.

Equator

Reason — Lines of longitude converge at the poles and are farthest apart at the Equator. Consequently, the distance between two meridians reaches its maximum of about 111 km at the Equator and gradually decreases to zero at the poles.

Both A and R are true and R is the correct explanation of A.

Explanation — Noon occurs when the sun is exactly overhead on a meridian, so all places along the same meridian experience noon at the same time. The sun appears to move from east to west across the sky and crosses the meridian at its highest point, which is why this moment is called noon.

24

Reason — To overcome the confusion caused by varying local times, the earth has been divided into 24 Time Zones according to the number of hours in a day. Each zone covers 15° of longitude (360° ÷ 24).

Uniform time based on a central meridian

Reason — The Standard Time is the uniform time of a country or region fixed with reference to a central meridian. It avoids the confusion that would arise if every place within a country followed its own local time.

All of the above

Reason — The International Date Line follows the 180° meridian, directly opposite the Prime Meridian, where crossing it changes the calendar date by one day. It is intentionally drawn in a zig-zag pattern near areas like the Bering Strait, Fiji, Tonga, and New Zealand to prevent a single country or island group from being split into two different days.

A is true but R is false.

Explanation — The Earth makes a complete circle on its axis — it covers 360° longitudes in 24 hours. That is to say, it covers every 15° longitudes in one hour or 1° longitude every 4 minutes. The earth rotates on its axis from West to East.

Crossed the IDL

Explanation — When you cross the International Date Line (IDL) from west to east, you lose a day because the calendar moves back by one day. The IDL is an imaginary line where the date changes by one day when crossed.

12:00 noon

Explanation — Fiji is about 12 hours ahead of Greenwich Mean Time (GMT). So, when it is midnight (12:00 am) in Fiji, it would be 12 hours earlier — that is 12:00 noon of the previous day in London (GMT).

equal to the radius of the sphere

Reason — A great circle is a circle drawn on a sphere's surface whose radius and center are identical to those of the sphere itself. It represents the largest possible circle that can be drawn on a globe, bisecting the sphere into two equal halves.

Both (1) and (3)

Reason — A great circle must pass through the centre of the earth. The Equator is the only line of latitude that passes through the centre, and all lines of longitude (as diametrically opposite pairs) also pass through the centre. Hence both the lines of longitude and the Equator are great circles, while all other parallels of latitude are small circles.

Both A and R are true and R is the correct explanation of A.

Explanation — The line of longitude 180° or IDL is one and the same for East or West of the Prime Meridian. Since it is diametrically opposite to the Greenwich Meridian it causes a time difference of a full day on crossing the line. The time difference works out to 12 hours (180° x 4 min) from either side. Thus, on crossing the line, a day is gained or lost.

A is true but R is false.

Explanation — A Great Circle Route is the shortest distance between two places on the earth and lies on the arc of a great circle. Using this hypothesis, navigators find the shortest distance between any two points on the earth's surface.

82½°

Explanation — World Standard Time is fixed with reference to the Prime Meridian, whose value is 0°. Similarly, Indian Standard Time is fixed with reference to the Standard Meridian of India, whose value is 82½°E.

6:30 am

Explanation — India is 5½ hours ahead of GMT. So, when the Indian Standard Time is 12:00 pm (noon), the Greenwich Mean Time will be 12:00 noon − 5:30 hrs = 6:30 am.

Prime Meridian

Explanation — Indian Standard Time is fixed with reference to the Standard Meridian of India (82½°E). In the same way, World Standard Time is fixed with reference to the Prime Meridian (0°).

A framework of lines of longitude and latitude on a globe or a map is called a geographic grid.

This grid on the globe or the map serves the same purpose as the system of coordinates on the x-axis and y-axis on a graph paper. In this case the x-axis is represented by lines of latitude (horizontal) and y-axis, by lines of longitude (vertical). These lines help to locate places on the earth.

Lines of latitude are imaginary lines that run east to west, parallel to the Equator. Lines of longitude are imaginary lines that run north to south, passing through the poles. This geographic system of coordinates was originally devised by the Greek philosopher Eratosthenes.

Two characteristics of lines of latitude are:

1. Lines of latitude are imaginary lines joining all places having the same latitude towards north or south of the equator.
2. A latitude is marked in degrees, with equator being 0 degrees.

The two hemispheres of the earth made by the Equator are-

1. Northern hemisphere
2. Southern hemisphere

The thermal zones of the earth are-

1. Torrid or Tropical zone
2. Temperate zone
3. Frigid zone

Two uses of the lines of latitude are:

1. To find the location of a Place — Latitudes give us the location of a place north or south of the Equator. Such a location is known as an absolute location.
2. To measure the distance of a Place — Distances are calculated with reference to the Equator at right angle to the place. We can therefore, measure the distance of any place from the Equator based on its degree of latitude.

The angular distance of 1° latitude is equal to 111 km.

The Prime Meridian is the line of longitude whose angular distance is defined as 0 degrees. It passes through Greenwich near London.

While fixing the Time Zones, the time at Prime Meridian has been selected as the mean time. The time for all the other places is calculated with reference to the time at Prime Meridian.

Lines of latitude divide the earth into three distinct heat belts -

1. Torrid zone, being the hottest zone
2. Temperate zone with moderate climate
3. Frigid zone with the coldest climate

The lines of latitude indicate the general climate of the area by applying the principle of heat zones of the earth.

Prime Meridian is used to fix the World Standard Time.

Its value in degrees is 0°.

The longitudinal value of Indian Standard Meridian is 82° 30'E.

Two characteristics of the Great Circles are:

1. All such circles must pass through or touch the centre of the circle.
2. Infinite number of circles that touch the two opposite ends of the sphere can be drawn on a sphere.

Two uses of the Great Circles are:

1. Great Circle routes are specially important for places that are on opposite sides of the globe. Most globes show great circle routes between distant ports across the Atlantic, the Pacific and the Indian Ocean.
2. Great circles are used by meteorologists to determine climate and weather conditions in a region.

A great circle route is the shortest distance between two places on the earth and lies on the arc of a great circle.

Great Circle Routes are specially important for places that are on opposite sides of the globe.

The main five lines of latitude are-

1. Equator (0°)
2. The Tropic of Cancer (23.5° N)
3. The Tropic of Capricorn (23.5° S)
4. The Arctic circle (66.5° N)
5. The Antarctic circle (66.5° S)

These lines of latitude form one of the coordinates of the grid system. The lines of latitude have the following significance-

1. They are used to find the location of a place
2. They are used to measure the distance of a place
3. They divide the earth into distinct heat zones

(i) Lines of latitude are called parallels of latitude as these lines are parallel to the Equator and each other.

(ii) Lines of latitude are not of equal length as they become smaller as we move towards the poles.

(iii) Lines of latitude carve out the heat zones of the earth as the temperature goes on decreasing from the equator towards the poles. Thus, these lines indicate the general climate of an area by applying the principle of heat zones.

The imaginary lines running north to south passing through the poles are called lines of longitude.

The earth makes a complete circle on its axis covering 360° in 24 hours. It covers 1° longitude every 4 minutes. For each 1° longitude towards the east, 4 minutes are to be added and for each 1° longitude towards the west, 4 minutes are to be subtracted.

(i) Lines of longitude are called meridians of longitude because the sun crosses a meridian at noon. So, all places on a particular meridian will have noon at the same time.

(ii) Lines of longitude are of same length as they all converge at the poles.

(iii) Diametrically opposite lines of longitude and the Equator are called Great Circles because they pass through or touch the centre of the circle. Also, they have a radius equal to the radius of the sphere's centre.

The line of longitude 180° is one and the same for east or west of the Prime Meridian. Since it is diametrically opposite to the Greenwich Meridian, it causes a time difference of a full day on crossing the line.

The International Date Line is the 180° line. When crossing this date line from the west to east a day is deducted or the time is fixed backward by one day. When crossing the International Date Line, from east to west, a day is added.

The International Date Line is the 180° line. When crossing this date line from the west to east a day is deducted or the time is fixed backward by one day. When crossing the International Date Line, from east to west, a day is added.

For example, if it is 8 pm Monday 25th December at Greenwich, it will be 8 am Tuesday, 26th December on crossing the 180° line from the east as time will be 12 hours ahead. But if one were to travel from west, it will be 12 hours behind or 8 am Monday, 25th December.

(i) The International Date Line deviates and goes zig-zag near some islands in the Pacific Ocean to avoid the confusion of having different dates within the same country.

(ii) The Greenwich time is called the Greenwich Mean Time as while fixing the time zones, the time at Greenwich has been selected as the mean time and provides the basis for calculating the Standard Time of other places.

(iii) Great Circles are the shortest routes between two places as we can connect any two places on the earth's surface by the curvature line of the great circle. And this curvature is the smallest possible route between those two places, because this curvature directly connects those places or points.

As the earth takes 24 hours to make a complete rotation along its axis crossing 360° lines of longitude, so earth takes nearly 4 minutes to move 1° longitude.

For example, Indian Standard Time is based on 82 1/2° E longitude. So if the time in India is 12 noon, so it will be 6.30 A.M. in England or GMT.

The time difference between 0° and 82 1/2° E will be-
82.5 × 4 = 330 minutes or 330 ÷ 60 = 5 1/2 hours

So there is difference of 5 1/2 hours between India and England, as England lies in the west, so the time will be 5 1/2 hours less than India.

The local time at Mumbai is 7:30 pm.
The location of Mumbai is 82 1/2° E of Prime Meridian.
The GMT would be 2:00 p.m. [7:30 hrs - (82 1/2° x 4 min) = 7:30 hrs - 5:30 hrs = 2:00 pm].
Ivory Coast is located at 20° W of Prime Meridian.
At any point of time, Ivory Coast will be 20 X 4 = 80 min = 1:20 hrs behind GMT.
So, when it is 2:00 pm at GMT, the local time at Ivory Coast will be 2:00 - 1:20 = 12:40 pm.

The time difference between the two places is 9:15 hrs (540 + 15 = 555 min).
So the longitudinal difference will be 555/4 = 138.75° degrees.
The longitude of the required place will be 50° 45′ E i.e. it will cover 88° from west to 0° and 50° 45 east from 0° or Greenwich line.

The longitudinal difference between Durban and New York is 30° + 75°= 105°.
The time at Durban will be ahead of New York by 420 minutes(105 x 4 min) or 7:00 hrs.
So, the time at Durban will be 2:00 pm (7:00 am + 7:00 hrs).

The difference in the time of both the longitudes is 15:00 hrs or 900 min.
The difference in longitudes will be 225° (900/4)
So the longitude will be 225° – 77° = 148°.
So the place will be to the west of New Delhi as New Delhi is ahead in time.
Thus, the longitude of a place where the local time is 6:00 a.m. will be 148° W.

Greenwich is 0° longitude.
The time difference between 0° and 104°E will be 416 min (104 x 4) or 6:56 hrs.
Singapore lies to the east of Prime Meridian so the local time will be 6:56 hrs ahead of GMT.
The local time at Singapore is 12:56 am (6:00 pm + 6:56 hrs)

The local time of the place is 12:00 pm.
The GMT is 7:30 pm.
The difference in time is 7:30 hrs or 450 min.
The difference in longitudes will be 112.5° (450/4).
Since the time at given place is less than GMT, the place is to the west of GMT.
So, the longitude of a place where the local time is noon is 112.5° W.

The difference in longitudes of Mumbai and Shillong is 19°.
The time difference between the two places will be 76 min (19 x 4) or 1:16 hrs.
Since, Mumbai lies to the west of Shillong, The time at Mumbai will be 1:16 hrs behind Shillong.
So, the time at Mumbai will be 9:14 pm (10:30 pm - 1:16 hrs).
The day will remain Sunday.

Note: All the places in India use IST as reference for time and Mumbai and Shillong both are located in India. Hence, there will be no difference in the time. The time will be the same and day will also be the same for both the places.

The latitude of my city is 26° 55' N.

My city lies in the North Temperate zone which is between 23½°N to 66½°N. This region experiences moderate climate i.e., the temperature is neither too hot nor too cold.

My home town is located near the poles as it receives slanting rays of the sun. Slanting rays lose more heat while travelling and result in cooler temperature. On the other hand, my boarding school is located near the equator as it receives vertical rays of the sun resulting in higher temperature.

Russia has the maximum number of time zones in the world, with a total of 11 time zones. The reason behind a country having multiple time zones is due to its geographical size and location. As the earth rotates, each 15° change in longitude corresponds to a one-hour difference in time. Therefore, a country that spans several longitudes, like Russia or the United States, may have multiple time zones to account for the variations in local time.

In the case of India, the country is geographically smaller and spans fewer longitudes compared to a country like Russia. Therefore, India has one time zone to maintain uniformity across the country.

Some countries like Australia, New Zealand, and Japan welcome the New Year before India because of the differences in time zones. These countries are located ahead of India in terms of longitude, and therefore, they are several hours ahead in time.

Australia and New Zealand are located in the eastern hemisphere and are ahead of India in terms of time zones. Japan is located in the same time zone as Australia and also welcomes the New Year before India.

1. 82 1/2° E
2. Tokyo - 5:30 am
   London - 9:30 pm
   San Francisco - 1:30 pm
3. Chile is diametrically opposite of India.
4. Yes, Indian Standard Time is ahead of San Francisco Time as India is 5:30 hrs ahead of GMT while San Francisco is 7:00 hrs behind GMT.