A coordinate system is a reference framework for representing geographic locations, using various measurement frameworks and units such as geographic (spherical) and planimetric (2D). Geographic coordinate systems use a 3D spherical model and include key elements like angular units and a datum, while projected coordinate systems transform these into a 2D plane. The document explains latitude and longitude concepts, their measurements, and different formats, along with types of coordinate systems like global and projected systems.

1. Basic Coordinate System
By
Saad Khan

2. What is a coordinate system?
• A coordinate system is a reference system
used to represent the locations of geographic
features, imagery, and observations, within a
common geographic framework.
• Coordinate systems enable geographic
datasets to use common locations for
integration.

3. What is a coordinate system?
Each coordinate system is defined by:
• Its measurement framework,
– geographic (in which spherical coordinates are measured from the
earth's center) or
– planimetric (in which the earth's coordinates are projected onto a
two-dimensional planar surface)
• Units of measurement (e.g. feet/meters for projected coordinate
systems or decimal degrees for lat/long)
• The definition of the map projection for projected coordinate
systems
• Other measurement system properties such as a spheroid of
reference, a datum, one or more standard parallels, a central
meridian, and possible shifts in the x- and y-directions

4. Types of Coordinate Systems
• A global or spherical coordinate system such
as latitude-longitude.
– Also referred to as geographic coordinate systems.
• A projected coordinate system such as (UTM),
represented by Cartesian coordinate plane.
– Projected coordinate systems are referred to as
map projections.

5. Geographic Coordinate Systems
• A geographic coordinate system (GCS) uses a
3D spherical surface to define locations on the
earth.
• A GCS includes an angular unit of measure, a
prime meridian, and a datum (based on a
spheroid).
• The spheroid defines the size and shape of the
earth model, while the datum connects the
spheroid to the earth's surface.

6. Positions on Globe: Lines of
Reference
Figure: 1
Figure: 2
Figure: 3
graticules

8. Latitude
“Latitude is the angular distance of any point
on Earth measured north or south of the
Equator in degrees, minutes and seconds”
• At poles (North and South Poles)
latitudes are 90o North and 90o South
• At equator latitude is 0°
• The equator divides the globe into
Northern and Southern Hemispheres
• Each degree of latitude is approximately
69 miles (111 km) (variation because
Earth is not a perfect sphere)
90° N
90° S
0°

9. Lines of Equal Latitudes
• Lines of constant latitude are called parallels of latitude (horizontal
lines)
• Parallel lines at an equal distance
• On Globe lines of latitude are circles of different radii
• Equator is the longest circle with
zero latitude also called ‘Great
Circle’ (24,901.55 miles)
• Other lines of latitudes are called
‘Small Circles’
• At poles the circles shrink to a
point
• Circle of Equator is divided into
360 degrees
In figure, lines of Latitude or Parallels

10. Some Important Small Circles
• Tropic of Cancer
– At 23.5°N of Equator and runs through Mexico,
Egypt, Saudi Arabia, India and southern China.
• Tropic of Capricorn
– At 23.5°S of Equator and runs through Chile,
Southern Brazil, South Africa and Australia.
• Arctic and Antarctic Circles
– At 66° 33′ 39″ N and 66° 33′ 39″ S respectively

11. Map of the World

12. Longitude
“Longitude is the angular distance of any point
on Earth measured east or west of the prime
meridian in degrees, minutes and seconds”
• Measured from 0° to 180° east and 180° west (or -
180°)
• The meridian at 0° is called Prime Meridian located
at Greenwich, UK
• Both 180-degree longitudes (east and west) share the
same line, in the middle of the Pacific Ocean where
they form the International Date Line
• 1 degree of Longitude=
– 69.17 mi at Equator
– 48.99 mi at 45N/S
– 0.0 mi at 90N/S
W 180° 180° E
Prime
Meridian

13. Lines of Equal Longitude
• Lines of Longitude (vertical lines/meridians)
• They are also called Meridians
• Meridians converge at the poles and are widest at the equator
about 69 miles or 111 km apart
• On Globe lines of longitude are circles of
constant radius which extend from pole
to pole
In figure, lines of longitude or meridian

14. Prime Meridian
• Royal Astronomical Observatory in
Greenwich, England
E W
S

15. Latitude/Longitude Formats
• Lat/long coordinates can be specified in different
formats:
1. DD.MM.SSXX (degree, minute, decimal second)
2. DD.MMXX (degree, decimal minute)
3. DDXX (decimal degree)
How to convert degree, minute, decimal second format
into decimal degree?
– Decimal degree = (Seconds/3600) + (Minutes/60) + Degrees
• In class exercise: DD conversion of24° 48' 58” N 66°
59' E

16. Quiz 2 (a)
1. DD conversion of 38° 20' 20” N 70° 56' 04” E is
_______________ N and ______________ E
2. DD conversion of 35° 38' 20” S 134° 56' 59” E is
_______________ S and ______________ E
3. The DMS version of 5.23456° is _________________

17. Projected Coordinate Systems
• A projected coordinate system (PCS) is defined
on a flat, 2D surface.
• A PCS is always based on a GCS that is based
on a sphere or spheroid.
• Projected coordinate system can be local (e.g.
NAD83) or global (UTM).

18. Projected Coordinate Systems
• Projected coordinates are described my
Cartesian values.

19. NAD83

20. UTM