Planet Earth: Representation of the Earth

The Earth is our planet. Although it is a tiny part of the Universe, it is different from other planets as it is the only one we know to be able to sustain life. 

The Earth is one of the 8 planets in the Solar System, located  on one of the arms of the galaxy named the Milky Way. The Earth orbits around the Sun, the star of the Solar System. It takes around 365 days for the Earth to revolve around the Sun. As the Earth revolves around the Sun it tilts very slightly originating the seasons.

At the same time, the Earth rotates on its axis in a clock-wise movement (from west to east). It takes aproximately 24 hours for the Earth to rotate. This movement originates day and night

The Earth: Shape and dimensions

Althoug the force of gravity would pull the Earth into a perfect sphere shape, the fast rotation of planet Earth on its axis (an imaginary line running from the Nort Pole to the South Pole), reduces the effect of gravity on the Equator (an imaginary line that runs around the middle of the planet at its widest point). This movement causes the equator to bulge outwards while making the poles appear flattened. This gives the Earth the shape of a geoid (similar to a sphere but flattened at the poles).

The Earths's equatorial circumference (widest part of the Earth) is aproximately 40.777 km long. The Earth's polar circumference (from pole to pole) is aproximately 40.008 km long.

The surface of the Earth is not flat. Although Mount Everest is the highest place above sea level (8.844 meters), the most distant point from the center of the Earth is Mount Chimborazo in the Andes Mountain Range. This is caused by the equatorial bulge. 

The lowest point of the Earth is Challenger Deep into the Mariana Trench in the Pacific Ocean, at 11.034 meters below sea level.

The Earth: Geographic Coordinates

The Earth: Geographic Coordinates

As the Earth is a geoid (a sphere with flattened poles) it is very difficult to represent it on a flat surface. To solve this problem, geographers have created geographic coordinates to organize the surface of the Earth and map projections to  to show the surface of the three-dimensional geoid on a flat surface. 

Geographic coordinates are imaginary line, which means they do not really exist on the surface of the Earth, which help us to locate a point on the surface of the Earth and to calculate the distance between two points on the Earth's surface. 

This lines are the parallels and the meridians. They cross each othe forming an imaginary grid or network on the Earth's surface. 

Cartographic Projections

The best way to represent the Earth is a globe. A terrestrial globe is a spherical model of Earth that do not distort its surface. However, terrestrial globes are not very useful to study parts of the Earht in detail.

 

To solve this problem, geographers have created cartographic projections or map projections. A cartographic projection allows representing the three-dimensional geoid of the Earth on a flat surface which we call map. Maps are easier to store; they can show larger portions of the Earth's surface in detail; they are cheaper to produce, etc.

Nevertheless, projecting the surface of a geoid to a plane is not possible. Every projection changes the surface of the Earth in some way. This change is called distorsion

Geographers have created different types of projections for different purposes so that the distorsion they create may not be very important for that purpose. 

Types of map projection: 

  • Cylindrical projection

  • Conic projection

  • Zenithal projection

Types of distortion: 

  • Equivalent projection

  • Conformal projection