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Lecture 2

GEG1301 Lecture 2: Overview of Earth

Course Code
GEG 1301
Denis Lacelle

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3 - Overview of Planet Earth
September 16, 2015
- Most of the landmass is found in the Northern Hemisphere
- 6 continents, covering 29% of Earth’s surface
Africa: Lacks mountains ranges (Has mountains, but no ranges)
South America: Mountain range on west, sloping basin in east
NA: Mountain range on west, and along the east (creates a funnel)
Blocks West-East movement of air, amplifies North-South
Eurasia: Mountain range extends from East to West
Australia: Mountain range on West
Antarctica: Mountain range along west
- Only ~ 1/3 of landmass are habitable by humans
- Ocean basin: Pacific, Atlantic (N & S), Indian, Southern, Arctic, and Mediterranean Sea
- Components of ocean basin:
Continental margins
Continental shelf, continental slope, continental rise
Abyssal zone
Abyssal plains, seamounts, mid-oceanic ridges
The continental shelf was not always submerged [Bering Strait land bridge]
- East-West hemispheres are defined by the Greenwich meridian
- Erasthenes: Calculated the circumference of the Earth (within 1.5% accuracy)
- Earth is not perfectly spherical, there is a bulge at the equator (geoid)
- Parallels (latitude) represent the angle relative to the equator
5 key parallels: Equator, Tropic of Cancer, Tropic of Capricorn, Arctic circle and
Antarctic circle
- Meridians (longitude) represent the angle relative to the prime/Greenwich meridian
All meet at the North and South poles
- The distance between two parallels is roughly equal regardless of latitude, but the
distance between meridians decreases as you approach the poles
- Coordinate systems:
Degrees, minutes, seconds (DMS)
45o45’34” N (max minutes & seconds is 60)
Decimal Degree (DD)
45.7594o N
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- Map: A generalized view of an area, seen from above & reduced in size
- Showing scale on maps:
Representative fraction is always unit less as the units are the same for both
values (can be anything)
Graphing scale/scale bar, not skewed by resizing
Written scale: one cm = 2.5 km
- Small-scale maps: Illustrate a large territory ex. the Earth, a country, a province etc.
Ex. 1 : 1,000,000 (1/1,000,000 is a very small number)
- Large-scale map: Illustrate a small territory, in great detail ex. regional or local maps
Ex. 1 : 50,000 (1/50,000 is larger)
- Projecting the globe onto a map causes distortion, the trick is to minimize distortion
5 main distortions: Scale, Area, Shape, Direction and Distance
You can preserve some of these features, but not all of them
- Ottawa is in UTM zone 18
- Maps use points, lines and/or polygons to convey information
Remote sensing
- Active and passive remote sensing
Active: Instrument sends out energy which is reflected back to it
Echolocation, Radar, Lidar
Allows us to see through clouds
Radarsat: maps arctic ice
Passive: Receives solar (or other) energy [visible light, thermal energy]
Cameras and sensors, eyes
Cannot penetrate clouds
Images cover a large variety of scales, which have their own advantages &
Landsat 30m resolution, less expensive, images from many years (since
mid 1980s) and geographic regions, images available free online
Ikonos 30cm resolution, very detailed, but very expensive, images are
only of small areas, images are very large (data-wise) so require high-
power computers to process
- Air photographs: Plane flies in straight line at constant altitude, with 50-60% overlap
Overlap between flight lines in 20-30%
Used to determine surface geography/vegetation
Are timely and costly to produce, so are only taken every 5 (or more) years
Some features are easy to interoperate (streams/rivers), while other are much
harder (types of vegetation, soil composition)
Overlap allows for stereoscopic (3D) viewing
Allows to estimate the elevation of various features
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