Chapter 2: Geographic Grid - Latitudes and Longitudes

Syllabus:

(a) Concepts of latitudes, their location with degrees, parallels of latitude and their

uses, Hemispheres- northern and southern

(b) Using latitudes and longitudes to find location

zones, GMT, IDL) Hemispheres- eastern, western, northern and southern

(d) Calculation of time

(e) Great circle and their uses

(a) Concepts of latitudes, their location with degrees, parallels of latitude

and their uses

Geographic Grid System

Geography is about spatial understanding, which requires an accurate grid system to determine

absolute and relative location.

➢ Absolute location is the exact x– and y– coordinate on the Earth.

➢ Relative location is the location of something relative to other entities

For example: when you use your GPS in your smart phone or car, say on Google Maps, you put

in an absolute location. But as you start driving, the device tells you to turn right or left relative

to objects on the ground: “ 200 meters Turn towards left ” is relative location. Or if you give

directions to your house, you often use relative locations to help them understand how to get to

your house.

➢

The geographic grid is used to locate places on a map or a globe.

The grid is a series of criss- crossed lines

Grids on a globe & map

Latitude: it is the angular distance of a place north or south of equator measured in degrees and

indicated with the letter N or S.

Line of Latitude : the series of lines drawn from east to west and are parallel to the equator is known as

lines of latitude or parallels of latitude. . These lines intersect at right angle therefore the distance from

these reference lines are measured in angle and indicated as degrees. ( they are not linear units such as

cm, km, feet , mile etc)

- the line which joins all the places having the same angular distance north or south of equator.

Eg: 40º N

- All lines of latitudes are circles parallel to the equator. Therefore they are called as parallels of

latitude

Equator :

⚫It is the imaginary line which lies mid way between the two poles.

⚫The plane of the equator intersects the earth’s axis at right angles.

⚫It is the longest line of latitude and it dive earth into two equal halves, therefore it is a ‘great circle’.

⚫Equator is the reference line used to measure the distance to the north and the south.

⚫Equator is taken as 0º latitude. Latitudes are measured form 0 to 90 degree in the north and 0 to

90 towards the south. 1 degree of latitude is equal to 111 km or 69 miles.

⚫The circumference of the earth ( distance around the circle) is 40000km . therefore 1º latitude is

equal to 40000 = 111 km ( around)

360º ( 24 hours)

Poles: Poles are the end point of axis .

➢North pole : the pole which points towards the pole star

➢South pole : the opposite of north pole

Axis: The imaginary line on which earth spins.

Northern hemisphere – The place of earth above the equator to the North pole

Southern hemisphere : The place of earth below the equator to the south pole

Important lines of Latitude

Besides the equator (0°), the North Pole (90°N) and the South Pole (90° S), there are four important

parallels of latitudes–

➢Tropic of Cancer (23½° N) in the Northern Hemisphere.

➢Tropic of Capricorn (23½° S) in the Southern Hemisphere.

➢Arctic Circle at 66½° north of the equator.

➢Antarctic Circle at 66½° south of the equator.

Heat Zones or Climatic Zones

➢ The Frigid Zone, Temperate Zone, and Torrid Zone are the three different heat zones of the

Earth.

➢ The Torrid Zone is the hottest, since it is closest to the equator.

➢ The temperate zone is the most comfortable zone for living and working because they are

neither too hot not too cold.

➢ The frigid zone is the coldest zone. Because of the tilt of the axis it is impossible for slanting rays

of Sun to reach beyond arctic circle from 23rd sept to 21st march and antarctic circle from 21st

march to 23rd sept. therefore these areas will have 6 months of darkness and six months of

light.

➢ Countries at the poles have 6 months day, and 6 months night. So countries close to these

region have such cases like, Alaska, Antarctica, Norway etc. Norway, the northernmost inhabited

region of Europe, there is no sunset from approximately 19 April to 23 August.

Fun Fact

Which country is known as ‘land of midnight sun’? Why?

Antarctica has six months of daylight in its summer and six months of darkness in its winter

(c)Concepts of longitudes – Prime Meridian, time ( local and standard, time zones, GMT, IDL)

Longitude: is the angular distance of a place east or west from Prime meridian.

Line of Longitude : the imaginary line drawn from the north pole to the south pole is known as

meridians of longitude/ line of longitude. Meridians converge at poles.these lines join all the places

having same angular distance measured in degrees along the equator east or west of prime meridian.

Line of longitudes are called meridians because all the places in the same line of longitude experience

mid day at the same time.

Prime Meridian or the Greenwich meridian :

is the line of reference for measuring the east- west distances. It is measured as 0 °.

There are 360 meridians. 180 meridians towards the east and 180 meridians towards the west from the

Prime meridian. These are imaginary lines.

The location of Prime Meridian was agreed upon by geographers from around the world who met in

Washington DC at 1884. The meridian passed through an ancient observatory where for centuries

astronomers had studied and familiar with the location so all world nations are agreed for it as GMT.

The Royal Observatory London

International Date Line :it is the 360th meridian is numbered as 180 °E & 180 ° W and lie just opposite

to the prime meridian makes a complete circle. Date and time differs in this circle.

On either side of the IDL there is a time difference of one day or 24 hours. The person who crosses the

line from east to west will lose a day and the person who crosses the line from west to east will gain a

day.

To avoid this time confusion, this line is not a straight line . It deviates all the land areas and marked in

the ocean.

Eastern Hemisphere: the zone between Prime meridian and 180 ° E is known as eastern hemisphere

Western Hemisphere : the zone between Prime meridian and 180 ° w is known as Western hemisphere

(b) Using latitudes and longitudes to find location

➢The crisscrossed lines on a map/ globe are lines of latitude and lines of longitude. These are

imaginary reference lines adopted on a uniform basis by all the countries to avoid confusion.

➢The intersection of lines of latitude and lines of longitude give exact position of a place on a map or

a globe.

➢The distance between two successive meridians will decrease gradually and the lines will merge at

poles due to the curvature of the earth.

➢The distance between two successive latitudes remains same because they are parallel to each

other..

Eg: the position of Delhi is indicated by 28 º 40 N

̍ and 77 º 14 E̍

Means Delhi is located 28 degree and 40 minutes north of the equator and 77 degree 14 minutes east of

the prime meridian based on the rotation of the earth. the position of Delhi is at he intersection of 28 º

40 N

̍ latitude and 77 º 14 ̍ longitude.

(a) Calculation of time

➢ Due to the spherical surface one half of the earth is illuminated by the Sun at a

given time and experiences day whereas the other half remain as dark and

experiences night.

➢ As the earth moves from west to east the part of illumination slowly moves

towards the west. This accounts for the variation in the time of sun rise and sun

set at different places on earth.

➢ Prime meridian is the basic meridian for the calculation of time on earth.

Formula for Calculation of time

Earth takes 24 hours to complete one rotation of 360º.

1 hour = 360/24 = 15º meridians

Time for 1 º = 60 minutes ( 1 hour) / 15 = 4 minutes

Note: time difference should be added for places located east and time difference

should be subtracted for the places located west of prime meridian to get the

correct time.

1. Example :

When it is 12 noon on Monday at GMT what is the local time at Tokyo ( 140 º E) ?

Difference in time :

140 x 4 = 560 minutes ie, 9 hrs 20 minutes

12 noon + 9 .20 hrs = 9.20 pm in Tokyo

Local time & Standard Time

Local time is the fixed time based on each meridian. It varies from one meridian to

another by 4 minutes. This can create confusion in the formal functioning of a

country.

India : between 8°4'N and 37°6'N latitude and 68°7'E and 97°25'E longitude

GMT / UTC ( Greenwich Mean Time & Coordinated Universal Time) : The

Greenwich mean time is based on the local time of the Greenwich meridian

passing through London. It is adopted by all the world countries for international

travel.

Standard time: the uniform time based on the standard meridian or the central

meridian of a country which is linked with the GMT or UTC is known as standard

time. The standard meridian of every country is linked with the GMT.

Indian Standard Time: The standard meridian of India ( IST) is 82° 30 'E is the

central meridian which passes through Allahabad or Prayagraj in Uttar Pradesh.

It is 5hrs and 30 minutes ahead of UTC.

Time Zones : As per the international agreement one time zone covers 15° of

longitudinal extent so whole world is divided into 24 time zones.

360/24 = 15

Small countries are located in single time zone because they adjusted the

boundaries of the time zones to suite their territorial convenience.

Large countries like Russia, USA and Canada have vast longitudinal extension so

they have more than one time zone.

Canada – 6 time zones

Russia – 11

USA – 5

(b) Great circle and their uses

Great circle is a circle drawn on the earth in such a way that the center of the

circle is the center of the earth.

➢ All the meridians of longitudes are great circles. Equator is the only line of

latitude which is a great circle.

Uses of great circles:

➢ They are of importance to aviation and navigation. The shortest route

between any two places is the arc of the great circle which passes through

them.

➢ Ships crosses vast oceans follow the great circle to save fuel and time.

➢ Air planes may not follow great circle routes due to territorial restrictions

imposed by the countries.