The geographic coordinate system is a spherical or ellipsoidal coordinate system for measuring and communicating positions directly on the Earth as latitude and longitude. It is the simplest, oldest and most widely used of the various spatial reference systems that are in use, and forms the basis for most others

1. Geographic
Coordinate
System
By Mahnoor Bukhari

2. Shape of the Earth
• Geodesy studies Earth’s shape, orientation, and positions for the past,
present, and future.
• It also studies where things are and where things are going to with extreme
accuracy.
• Models of Earth:
i. Spheroid
ii. Ellipsoid
iii. Geoid (true 3-D shape of Earth considered as a mean sea level extended continuously
through the continents)
• Geodesists have adopted an Ellipsoid model to determine Latitude and
Longitude coordinates.
a figure resembling a sphere. also : an object of approximately spherical shape.

3. Ellipsoid
• The Earth is an Ellipsoid.
• Because of the "bulging" caused by the Earth spinning, the Earth is not
completely round, thus, is not a sphere. Instead, we use the term
"oblate spheroid," or "ellipsoid."
• Earth Bulges at the Equator.
• We say Earth is a sphere… But it’s not exactly a perfect one.
• It’s an oblate spheroid that bulges at the equator and is somewhat
squashed at the poles.

4. Geoid and Ellipsoid Example

5. Earth’s Geographical
Coordinates
• Latitude and longitude, together forms Earth’s
geographical coordinates, and represents the
angular distance of any location from the center of
the Earth.
• A grid of parallels and meridians shown as lines
on a map is called a ‘graticule’.

6. Latitudes

7. • Any circle that runs east and west around Earth and that is parallel to
the equator is called ‘parallel’ or a ‘line of latitude’.
• All parallels (lines of latitude) except equator get smaller as you get
near the pole.
• Parallel but not equal.
• Five Important Latitudes:
• Arctic circle -----------------→ 66 1/2° N
• Tropic of cancer -----------------→ 23 1/2° N
• Equator -----------------→ 0°
• Tropic of Capricorn -------------→ 23 1/2° S
• Antarctic circle -----------------→ 66 1/2° S

8. Longitudes
(earth)

9. • Any semi-circle that runs north and south around Earth from the
geographic north pole to geographic south pole is called ‘meridian’ or
‘line of longitude’.
• The distance between longitudes reaches zero at the poles as the lines
of meridian converge at that point.
• Not parallel but equal.

10. And on the other hand, lines of
longitude have X-coordinates
between -180 and +180 degrees.
As shown in the image, lines of
latitudes have Y-values that are
between -90 and +90 degrees.

11. Explanation of Coordinate System
• When you put two coordinates together as a pair (X, Y), you can locate anything on Earth.
• Latitude and longitude form our coordinate system grid.
• Thanks to our geographic coordinate, you can pinpoint any point on Earth such as GPS
receivers.
• Cartographers write latitudes and longitudes in degrees-minutes-seconds (DMS) and
decimal degrees. For degrees-minutes-seconds, minutes range from 0 to 60. For example, the
geographic coordinate expressed in degrees-minutes-seconds for New York City is:
• Latitude: 40 degrees, 42 minutes, 51 seconds N
• Longitude: 74 degrees, 0 minutes, 21 seconds W
• You can also express geographic coordinates in decimal degrees. It’s just another way to
represent that same location in a different format. For example, here is New York City in
decimal degrees:
• Latitude: 40.714 N
• Longitude: -74.006 W

12. GPS Coordinates Pakistan
• Pakistan lies in the North-East part of the world
• 23 degrees 35 minutes to 37 degrees 05 minutes North (latitude)
• 60 degrees 50 minutes to 77 degrees 50 minutes East (longitude)

13. World Time Zones

14. UTC vs. GMT: History
• You'll often see UTC (Coordinated Universal Time) and GMT (Greenwich Mean Time) used
interchangeably, and while doing so can be suitable for informal use, they are not technically the same.
• GMT, or Greenwich Mean Time, is a time zone located along the prime meridian. It was established as
an international standard in 1884 at the International Meridian Conference, where many nations got
together to decide what the prime meridian of the Earth would be. Prior to this, time varied wildly in
different areas.
• The prime meridian selected at that conference runs through the Royal Observatory in Greenwich,
giving the time zone its name. From 1884 until the 1950s, GMT was used as the time standard.
• However, as atomic clocks were invented in the 1950s, there were more accurate ways of keeping time.
The new standard for coordinated time was first used at the beginning of 1960, but it didn't become an
official term until 1967 and replaced GMT a few years later.
• So, GMT is a time zone, while UTC is a time standard. You can consider UTC the successor to GMT, as
it's more accurate.

15. UTC or Coordinated Universal Time
• What Is UTC?
• UTC is the standard of time used all around the world to regulate clocks. It is
effectively the "center" of our timekeeping, with all time zones referenced in relation to
how far ahead of, or far behind, UTC they are.
• The full name for UTC is Coordinated Universal Time, and its initialism was reached
as a compromise. English speakers wanted to use CUT (for "Coordinated Universal
Time"), while French speakers advocated for TUC (short for "temps universel
coordonné"). Ultimately, UTC was chosen.

16. Time Zones Explained
• What are the Time Zones?
• Time Zones are a geographical division of the terrestrial globe into 24
longitudinal sections. The distance between two consecutive time zones is
approximately 15°. Each such time zone observes a uniform standard time.
• We have 24 different time zones in the world. Because the Earth rotates
360° every 24 hours, each time zone is 15° longitude apart from the other.
(360÷24=15)
• The Prime Meridian (Greenwich Meridian) defines the center of the first
time zone in the world

17. Irregular Time Zone Boundaries
• No time zone in the world runs a perfect north-south line. Instead, they
are jagged and adapt to the political boundaries of countries. Also,
there can be “irregular square” time zones similar to islands.

19. Name Description Relative to GMT
GMT Greenwich Mean Time GMT
UTC Universal Coordinated Time GMT
ECT European Central Time GMT+1:00
EET Eastern European Time GMT+2:00
ART (Arabic) Egypt Standard Time GMT+2:00
EAT Eastern African Time GMT+3:00
MET Middle East Time GMT+3:30
NET Near East Time GMT+4:00
PKT Pakistan Standard Time GMT+5:00
IST India Standard Time GMT+5:30
BST Bangladesh Standard Time GMT+6:00

20. Why do countries need different time zones?
• Maintaining different time zones for any country is not an easy choice.
From commercial and business transactions to transportation and
communication, everything is dependent on time. Thus, most countries
of the world have opted for one standard time zone. Some countries,
with comparatively larger areas or territories scattered around the
world, do opt for multiple time zones. For example, the USA, Russia
and Canada have multiple time zones within the country.

22. What is UTC Offset?
• UTC Offset is the time difference of a particular place from UTC. It is
measured in hours and minutes.
• For a place ahead of UTC (east of UTC), a positive sign is used.
Similarly, for a place which is located behind the UTC (west of UTC),
a negative sign is used.
• Example
• The time zone in Toronto (Canada) is UTC-4 while the time zone in
Beijing (China) is UTC+8.

23. Pakistan Time Zone
• Pakistan Standard Time (abbreviated as PKT) is UTC+05:00 hours
ahead of Coordinated Universal Time.

24. International Date Line
• The International Date Line is a north-south line in the Pacific Ocean
where you turn your calendar back or ahead one day. The center of the
time zone roughly follows 180° longitude without crossing any
landmass.
• When you cross the International Date Line moving toward the east,
you turn your calendar back one day. Whereas when you go from the
west across the International Date Line, you turn your calendar ahead
one day.

25. Thanks.