# § 15.Hradusna grid on the map and a map (textbook)

§ 15. Degree grid on the map and a map

Remember why the map Ptolemy was accurate on the map Eratosthenes.

On globe or a map you can see the line, held in a order. This - parallels and meridians.

Parallels. Нand globe and map at equal distance from the poles The circle - equator. Besides him there are other circles - parallels. The name "parallel" indicates the relative position of these lines Equator: parallels held strictly parallel to the equator. Equator is well parallel with the main. Since it is counting the other parallels that held by some distance in degrees in Northand Southern Hemisphere. Parallels - imaginary line that surrounds the globe west to east (or east to west). The parallel can be conducted through any point of the earth's surface. Thus,  parallels - A line that conditionally performed on the map and the map along the equator.

On the globe and map the parallels are not equal in length. Longest parallel - Equator. From it toward the poles of radius count is reduced and parallel decreases in length respectively. By size arc parallels can determine the distance, but remember that parallels -  circles, varying in length. Therefore, toward the poles will be reduced and Size 10 Parallels in kilometers. Most itbe near the equator - 111.3 km, on a mark, eg 600 - 55.8 km and the lowest - near the poles. Length 10 at different parallels marked hemispheres on the map on the right side of the frame.

Meridian. Word Meridian means "Poludenna line. Indeed, the direction of the meridian coincides with the direction of shadows from objects on the Earth's surface at noon. Meridian can carry through any point of the earth's surface, and everywhere it will be to north and south, ie the poles.

Meridian as well as the parallels are imaginary lines. They exist only on the Globe and maps. All meridians, extending from pole to pole, converging near poles, and then converge at the point of origin. Thus, мerydiany - Is the shortest line that conditionally held on map or globe from one pole to another.

All meridians are of equal length and shape of a pound. Part of the circle called arc, and the value of the arc measured in degrees. If a circle has 360 known0, then the arc - a half circle will have under-meridian half - 1800. Remember: the circle of the Earth (the equator) has 40 000 km, with half circle will be 20 000 km. Then you can calculate the length of 10 meridian in kilometers: 20 000 km: 1800 = 111 km. Knowing this, you can determine the distance on the map hemispheres in kilometers without scale, but only by degree meridians.

Consider examples. Length of arc of the meridian from the North Pole to the equator is 900. Thus, this distance will be: 900 x 111 km = 9990 km. That calculate, for example, length Africa20 th meridian, must do the following: 1) find on map section 20 th meridian within Africa, 2) find the value C endpoints mainland at this meridian (320 and 340) 3) calculate How many degrees mainland stretches on this meridian (320 + 340 = 660) 4) distance in degrees translate into miles (660 111 km x 326 km = 7.)

 Fig. Meridian Fig. Parallels

Degree mesh. Earth is covered with fine mesh like lines of meridians and parallels. Clearly, directly on the earth's surface this network there. She, like Earth's axis around which Earth rotates - imaginary. All of her lines - and there are only conditional on a globe and maps.

Meridian and can be conducted through a parallel anywhere in the earth's surface. The map and globe to carry through the same number of degrees, for example after 100or 200. Peretynayuchys, they form a grid Degree. Thus, Degree Grid - A grid on the map or map, parallels and meridians formed, which held through a certain number of degrees.

There differences of degree grid on the map and the map. On globe meridians - same semicircle, and parallels - various largest circle.

On different Maps parallels and meridians are represented differently. Thus, map hemispheres meridians depicted as a pound, and one in the middle Hemisphere - in a straight line. Parallels to map hemispheres - the arc and only one - the equator - a straight line. And on the map Ukraine all meridians are depicted as straight lines parallel - too little noticeably curved straight.

Why so different image of parallels and meridians? Because the transition from spherical form a globe to the plane of the map does not avoid distortion degree lines net.

Degree mesh allows to determine the direction of map. If the plan area to the north direction oriented precisely on top frame, then it maps show meridians. A parallel respectively indicate direction west-east. On the map side of the horizon into account when define the position of continents, countries, towns of more objects. For example, Antarcticalocated in the Southern Hemisphere, France- To the west of Europe, Crimean peninsula- In southern Ukraine.Degree grid lines to help locate objects.

Fig. Degree Grid

1. What are called parallels?

2. Which direction are parallel to the globe and map?

3. What is the value in degrees of latitude? And in kilometers?

4. Over the globe identify which parallels do not cross any continent.

5. What is called meridians?

6. Which direction are meridians on the map and the map?

7. What is the meridian crosses the Ural mountains almost in the middle?

8. What is the difference in the image of parallels and meridians on the globe and map?

9. Decide on the map hemispheres:

a) how many degrees is the arc of meridian from equator to the South Pole, b) how many degrees has the closest parallel to the pole;

c) how much C is closest to the equator parallel.

10. Decide on the length of the Southern hemisphere map America on 60 th meridian and 20 th parallel in degrees and kilometers.