Geography and History 1º ESO Unit 1- Planet Earth and its representation

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Unit 1- Planet Earth and its representation

CONTENTS

I. Planet Earth and its movements

II. Geographic coordinates

III. The representation of the Earth

IV. Maps

V. Time zones

I- Planet Earth and its movements

I am sure you all know everything about this issue, so it will be enough to take a look at

the power point in order to go over the first part of the unit.

II- Geographic coordinates

Parallels and Geographic meridians form an imaginary geographical network, which

allows us to locate the exact point of any place in the world, which are called latitude

and longitude. Therefore, lines of latitude and longitude form an imaginary grid over the

Earth's surface. By combining longitude and latitude measurements, any location on

earth can be determined.

If we add the altitude measurement, we would

have the three figures used in GPS (Global

Positioning System).

Geography and History 1º ESO Unit 1- Planet Earth and its representation

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The units of measurement for geographic coordinates

are degrees (°), minutes ('), and seconds ("), so:

– Like a circle, the Earth has 360 degrees.

– Each degree is divided into 60 minutes, which in turn

is divided into 60 seconds.

Moreover, latitude and longitude coordinates also

include cardinal directions:

– North or south of the equator for latitude,

– East or west of the prime meridian for longitude.

Parallels are imaginary circles perpendicular to the axis of the earth. They measure 360

degrees.

The Equator is the largest parallel and it divides the earth into two hemispheres: North

and South. We must notice that their number is infinite, although we only draw some of

them. They have E-W direction, and parallels and

meridians cut each other at a right angle. The main

parallels we can find in a world map are:

The meridians are imaginary maximum semicircles

drawn from the North Pole to South Pole. They

measure 180 degrees (half of a circle). The meridian of

reference (0 degrees) is Greenwich, whose name comes

from the astronomical observatory located near London.

Their direction is North- South and they have their

maximum separation in Ecuador and converge at the poles. They cut the parallels at

right angles.

Once we know what parallels and meridians are, we can mark any point on the Earth´s

surface, in other words, the latitude and longitude.

Latitude is the distance expressed in degrees, minutes and seconds, between any point

on the Earth's surface and the parallel 0º or Equator. It is measured northward or

southward. Its value is between 0 and 90 degrees.

On the other hand, longitude is the distance measured in degrees, minutes and seconds,

from any point on the Earth's surface and the meridian 0 (Greenwich). It is measured

east or west. Its value is between 0 and 180 degrees.

III- The representation of the Earth

Since the ancient past, people have used maps to represent the world. Have you ever

drawn the whole Earth? What problems did you have to draw it? The main problem is

trying to draw a three dimension object on a flat sheet of paper. Maybe the solution is to

Geography and History 1º ESO Unit 1- Planet Earth and its representation

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carry a globe inside our backpack before starting our trips...

Remember that Earth Globes are three-dimensional models

(having width, length and depth) that represent the Earth.

Unlike maps, the representation does not give rise to

deformities, expressing reality with more accuracy.

However, globes have a significant problem that makes

them less useful than maps: their poor mobility. Many

globes have drawings of the meridians and parallels, and an

inclined axis is often inserted to symbolize the inclination of

the Earth with respect to the sun.

I think you agree this is not the best solution, and since we know that the Earth is a

sphere, cartographers have tried to represent the 3D Earth in maps. That is the origin of

maps projections.

A map projection is the method to represent the Earth's surface on a plane. It's a system

which translates the meridians and parallels network from a curved surface as the Earth

globe to a flat surface.

There is no perfect method of projection; in fact, all of them distort reality in one way or

another. The use of one projection or another depends on the type and purpose of each

map. Let´s see some of the most important map projections:

https://www.youtube.com/watch?v=X4wgFSHZXBg

https://www.youtube.com/watch?v=eS-C8CcNa7M

Geography and History 1º ESO Unit 1- Planet Earth and its representation

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In conical or conic projections, the reference spherical surface is projected onto a cone

placed over the globe. The cone is cut lengthwise and unwrapped to form a flat map.

In cylindrical projections, the reference spherical surface is projected onto a cylinder

wrapped around the globe. The cylinder is then cut lengthwise and unwrapped to form a

flat map.

In planar (also known as azimuthal or zenithal) projections, the reference spherical

surface is projected onto a plane

The most popular projection has been the Mercator cylindrical one, made in the 16th

century. Mercator is the guilty of our false perception of our world, because the areas

near the Equator are is almost perfect, but there is a lot of distortion in the poles.

For that reason, and trying to represent more accurately the Earth, another cartographer

named Peters made a new projection.

What differences can you see between

both maps?

Try it before watching this video:

http://verne.elpais.com/verne/2015/04/14/

articulo/1429016086_681676.html

IV- Maps

A map is a true representation of the whole or part of an area on a flat surface, although

until recent times it was only of the world people knew.

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There are numerous types of maps, but, basically, two are emphasized: topographical

and thematic.

a) Topographical maps

Provide information about the physical elements or landscape, representing mountains,

rivers, lakes etc.

b) Thematic maps

These maps are very different, classified by the function of the issue that they represent:

- Political maps

- Physical maps

- Climate maps

- Demographic maps

- Economics

- Etc

Look carefully to this web:

https://www.nps.gov/webrangers/activities/readingmap/

We must know how to read and understand a map, don´t forget we use them very often.

First of all, we have to know how what the scale is: the ratio between the size of the area

represented on the map and the real size of the area. We can find two types of scale:

- Numeric scale: It is expressed as a fraction. The numerator represents a unit on

the map. The denominator represents its size in the real world.

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- Graphic scale: It is the way to relate the reality with the map. It is a bar divided

into equal segments (1 cm).

In this text you have a brief summary of the main elements you need to know to

read a map:

V- Time zones

The time zones are each of the 24 spherical sectors which divide the land area.

Each of them results to divide the 360º of the Earth globe between the 24 hours that

invests in giving a complete revolution on its own axis. Each time zone measured 15

degrees (360º / 24 hours = 15º, 15º = 1 hour).

The prime meridian or Greenwich meridian is the starting point for the times zones

around the world (GMT). Remember you have to add 1 hour for every time zone you

cross when travelling to the East, and subtract if you travel west.

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