Geodesy and Map
Projections 1
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Understanding Earth's Shape & Coordinate Systems: Geodesy, Longitudes, Latitudes & Maps, Lecture notes of Environmental Science
An introduction to geodesy, the study of the Earth's size, shape, and positioning of geographical points. Learn about the Earth's spheroid shape, coordinate systems, and longitudes and latitudes. Understand the importance of these concepts in Geographic Information Systems (GIS) for locating features, geographic analyses, and calculating time.
Typology: Lecture notes
2020/2021
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Geodesy and Map
Projections 1
Geodesy - Definition
- (^) Geodesy is the study of the earth’s size,
shape and the determination of the exact
position of geographical points e.g
longitudes, latitudes and elevation.
- (^) Geodesists is a person who specializes in
the study of geodesy
- (^) Geodetic refers to any activity or
measurement related to geodesy
Equatorial axis (a) is equal to Polar axis (b)
Equatorial axis (a) is greater than Polar axis (b)
Earth’s Shape cont’d
- (^) In actual fact, the earth’s shape is not that
smooth due to mts, valleys, plains and seas.
- (^) This rough structure of the earth is known as
the earth’s topographical surface or terrain.
- (^) An approximate representation of this true
earth’s surface is known as a geoid.
Coordinate Systems
- (^) A coordinate system is a set of lines or points
that are used for indicating the location of
features and places on the earth’s surface.
- (^) In GIS, there are two types of coordinate
systems:
- (^) Geographic coordinate systems
- (^) Projected coordinate systems
- (^) They are important for:
- (^) Locating features
- (^) Geographic analyses e.g calculations & measurements involving distances, areas, overlays, etc.
- (^) Calculating time: Determine time zones
Longitudes and Latitudes
- (^) Geographic coordinate systems uses longitudes and latitudes to locate features on a curved or plane earth’s surface.
- (^) Longitudes are defined as imaginary lines running from the north pole to the south pole and extending from east to west of the equator. They are also known as meridians.
- (^) Longitude 0o^ is a called the Prime or Greenwich meridian and is a reference longitude because it is the starting point for all other longitudes.
- (^) There are 180 lines of longitudes on both sides of
prime meridian.
- (^) All longitudes to the east of the prime meridian are given positive values while those to the west are negative.
Longitudes and Latitudes cont’d
- (^) The equator divides the earth into two regions
called hemispheres.
- (^) The region north of the equator is known as
the northern hemisphere while south of the
equator is known as the southern hemisphere.
- (^) The prime meridian also divides the earth into
two hemispheres.
- (^) West of the prime meridian is the western
hemisphere and east of the prime meridian is
the eastern hemisphere.
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