Determination of coordinates. Geographical coordinates

In Chapter 1, it was noted that the Earth has the shape of a spheroid, that is, an oblate ball. Since the earth's spheroid differs very little from a sphere, this spheroid is usually called the globe. The earth rotates around an imaginary axis. The points of intersection of the imaginary axis with the globe are called poles. North geographic pole (PN) is considered to be the one from which the Earth’s own rotation is seen counterclockwise. South geographic pole (PS) - the pole opposite to the north.
If you mentally cut the globe with a plane passing through the axis (parallel to the axis) rotation of the earth, then we get an imaginary plane called meridian plane . The line of intersection of this plane with the earth's surface is called geographical (or true) meridian .
A plane perpendicular to the earth's axis and passing through the center of the globe is called plane of the equator , and the line of intersection of this plane with the earth’s surface is equator .
If you mentally cross the globe with planes parallel to the equator, then on the surface of the Earth you get circles called parallels .
The parallels and meridians marked on globes and maps are degree mesh (Fig. 3.1). The degree grid makes it possible to determine the position of any point on the earth's surface.
It is taken as the prime meridian when compiling topographic maps Greenwich astronomical meridian , passing through the former Greenwich Observatory (near London from 1675 - 1953). Currently, the buildings of the Greenwich Observatory house a museum of astronomical and navigational instruments. The modern prime meridian passes through Hurstmonceux Castle 102.5 meters (5.31 seconds) east of the Greenwich astronomical meridian. A modern prime meridian is used for satellite navigation.

Rice. 3.1. Degree grid of the earth's surface

Coordinates - angular or linear quantities that determine the position of a point on a plane, surface or in space. To determine coordinates on the earth's surface, a point is projected as a plumb line onto an ellipsoid. To determine the position of horizontal projections of a terrain point in topography, systems are used geographical , rectangular And polar coordinates .
Geographical coordinates determine the position of the point relative to the earth's equator and one of the meridians, taken as the initial one. Geographic coordinates can be obtained from astronomical observations or geodetic measurements. In the first case they are called astronomical , in the second - geodetic . During astronomical observations, the projection of points onto the surface is carried out by plumb lines, and during geodetic measurements - by normals, therefore the values ​​of astronomical and geodetic geographical coordinates are somewhat different. To create small-scale geographic maps, the compression of the Earth is neglected, and the ellipsoid of revolution is taken as a sphere. In this case, the geographic coordinates will be spherical .
Latitude - an angular value that determines the position of a point on Earth in the direction from the equator (0º) to the North Pole (+90º) or the South Pole (-90º). Latitude is measured by the central angle in the meridian plane of a given point. On globes and maps, latitude is shown using parallels.

Rice. 3.2. Geographic latitude

Longitude - an angular value that determines the position of a point on Earth in the West-East direction from the Greenwich meridian. Longitudes are counted from 0 to 180°, to the east - with a plus sign, to the west - with a minus sign. On globes and maps, latitude is shown using meridians.

Rice. 3.3. Geographic longitude

3.1.1. Spherical coordinates

Spherical geographic coordinates are called angular values ​​(latitude and longitude) that determine the position of terrain points on the surface of the earth’s sphere relative to the plane of the equator and the prime meridian.

Spherical latitude (φ) called the angle between the radius vector (the line connecting the center of the sphere and a given point) and the equatorial plane.

Spherical longitude (λ) - is the angle between the prime meridian plane and the meridian plane given point(the plane passes through a given point and the axis of rotation).

Rice. 3.4. Geographic spherical coordinate system

In topography practice, a sphere with radius R = 6371 is used km, the surface of which is equal to the surface of the ellipsoid. On such a sphere the arc length great circle in 1 minute (1852 m) called.

nautical mile

3.1.2. Astronomical coordinates Astronomical geographic coordinates are latitude and longitude that determine the position of points on geoid surface

relative to the plane of the equator and the plane of one of the meridians, taken as the initial one (Fig. 3.5). latitude (φ) is the angle formed by a plumb line passing through a given point and a plane perpendicular to the axis of rotation of the Earth.

Plane of the astronomical meridian - a plane passing through a plumb line at a given point and parallel to the Earth’s axis of rotation.
Astronomical meridian - line of intersection of the geoid surface with the plane of the astronomical meridian.

Astronomical longitude (λ) is the dihedral angle between the plane of the astronomical meridian passing through a given point and the plane of the Greenwich meridian, taken as the initial one.

Rice. 3.5. Astronomical latitude (φ) and astronomical longitude (λ)

3.1.3. Geodetic coordinate system

IN geodetic geographic coordinate system the surface on which the positions of points are found is taken to be the surface reference -ellipsoid . The position of a point on the surface of the reference ellipsoid is determined by two angular quantities - geodetic latitude (IN) and geodetic longitude (L).
Geodesic meridian plane - a plane passing through the normal to the surface of the earth's ellipsoid at a given point and parallel to its minor axis.
Geodetic meridian - the line along which the plane of the geodesic meridian intersects the surface of the ellipsoid.
Geodetic parallel - the line of intersection of the ellipsoid surface with a plane passing through a given point and perpendicular to the minor axis.

Geodetic latitude (IN)- the angle formed by the normal to the surface of the earth's ellipsoid at a given point and the plane of the equator.

Geodetic longitude (L)- dihedral angle between the plane of the geodesic meridian of a given point and the plane of the initial geodesic meridian.

Rice. 3.6. Geodetic latitude (B) and geodetic longitude (L)

3.2. DETERMINING GEOGRAPHICAL COORDINATES OF POINTS ON THE MAP

Topographic maps are printed in separate sheets, the sizes of which are set for each scale. The side frames of the sheets are meridians, and the top and bottom frames are parallels. . (Fig. 3.7). Hence, geographic coordinates can be determined by the side frames of a topographic map . On all maps, the top frame always faces north.
Geographic latitude and longitude are written in the corners of each sheet of the map. On maps of the Western Hemisphere, in the northwestern corner of the frame of each sheet, to the right of the meridian longitude value, the inscription is placed: “West of Greenwich.”
On maps of scales 1: 25,000 - 1: 200,000, the sides of the frames are divided into segments equal to 1′ (one minute, Fig. 3.7). These segments are shaded every other and are divided by dots (except for a map of scale 1: 200,000) into parts of 10" (ten seconds). On each sheet, maps of scales 1: 50,000 and 1: 100,000 show, in addition, the intersection of the middle meridian and middle parallel with digitization in degrees and minutes, and along the inner frame - outputs of minute divisions with strokes 2 - 3 mm long. This allows, if necessary, to draw parallels and meridians on a map glued from several sheets.

Rice. 3.7. Side map frames

When drawing up maps at scales 1: 500,000 and 1: 1,000,000, a cartographic grid of parallels and meridians is applied to them. Parallels are drawn at 20′ and 40″ (minutes), respectively, and meridians at 30′ and 1°.
The geographic coordinates of a point are determined from the nearest southern parallel and from the nearest western meridian, the latitude and longitude of which are known. For example, for a map of scale 1: 50,000 “ZAGORYANI”, the nearest parallel located to the south of a given point will be the parallel of 54º40′ N, and the nearest meridian located to the west of the point will be the meridian 18º00′ E. (Fig. 3.7).

Rice. 3.8. Determination of geographical coordinates

To determine the latitude of a given point you need to:

• set one leg of the measuring compass to a given point, set the other leg at the shortest distance to the nearest parallel (for our map 54º40′);
• Without changing the angle of the measuring compass, install it on the side frame with minute and second divisions, one leg should be at the southern parallel (for our map 54º40′), and the other between the 10-second points on the frame;
• count the number of minutes and seconds from the southern parallel to the second leg of the measuring compass;
• add the result to the southern latitude (for our map 54º40′).

To determine the longitude of a given point you need to:

• set one leg of the measuring compass to a given point, set the other leg at the shortest distance to the nearest meridian (for our map 18º00′);
• without changing the angle of the measuring compass, install it on the nearest horizontal frame with minute and second divisions (for our map, the lower frame), one leg should be on the nearest meridian (for our map 18º00′), and the other - between the 10-second points on horizontal frame;
• count the number of minutes and seconds from the western (left) meridian to the second leg of the measuring compass;
• add the result to the longitude of the western meridian (for our map 18º00′).

note that this method of determining the longitude of a given point for maps at a scale of 1:50,000 and smaller has an error due to the convergence of the meridians that limit the topographic map from the east and west. The north side of the frame will be shorter than the south. Consequently, discrepancies between longitude measurements on the north and south frames may differ by several seconds. To achieve high accuracy in the measurement results, it is necessary to determine the longitude on both the southern and northern sides of the frame, and then interpolate.
To increase the accuracy of determining geographic coordinates, you can use graphic method. To do this, it is necessary to connect the ten-second divisions of the same name closest to the point with straight lines in latitude to the south of the point and in longitude to the west of it. Then determine the sizes of the segments in latitude and longitude from the drawn lines to the position of the point and sum them accordingly with the latitude and longitude of the drawn lines.
The accuracy of determining geographic coordinates using maps of scales 1: 25,000 - 1: 200,000 is 2" and 10" respectively.

3.3. POLAR COORDINATE SYSTEM

Polar coordinates are called angular and linear quantities that determine the position of a point on the plane relative to the origin of coordinates, taken as the pole ( ABOUT), and polar axis ( OS) (Fig. 3.1).

Location of any point ( M) is determined by the position angle ( α ), measured from the polar axis to the direction to the determined point, and the distance (horizontal distance - projection of the terrain line onto the horizontal plane) from the pole to this point ( D). Polar angles are usually measured from the polar axis in a clockwise direction.

Rice. 3.9. Polar coordinate system

The following can be taken as the polar axis: the true meridian, the magnetic meridian, the vertical grid line, the direction to any landmark.

3.2. BIPOLAR COORDINATE SYSTEMS

Bipolar coordinates are called two angular or two linear quantities that determine the location of a point on a plane relative to two initial points (poles ABOUT 1 And ABOUT 2 rice. 3.10).

The position of any point is determined by two coordinates. These coordinates can be either two position angles ( α 1 And α 2 rice. 3.10), or two distances from the poles to the determined point ( D 1 And D 2 rice. 3.11).

Rice. 3.10. Determining the location of a point from two angles (α 1 and α 2 )

Rice. 3.11. Determining the location of a point by two distances

In a bipolar coordinate system, the position of the poles is known, i.e. the distance between them is known.

3.3. POINT HEIGHT

Were previously reviewed plan coordinate systems , defining the position of any point on the surface of the earth's ellipsoid, or reference ellipsoid , or on a plane. However, these plan coordinate systems do not allow one to obtain an unambiguous position of a point on the physical surface of the Earth. Geographic coordinates relate the position of a point to the surface of the reference ellipsoid, polar and bipolar coordinates relate the position of a point to a plane. And all these definitions do not in any way relate to the physical surface of the Earth, which for a geographer is more interesting than the reference ellipsoid.
Thus, plan coordinate systems do not make it possible to unambiguously determine the position of a given point. It is necessary to somehow define your position, at least with the words “above” and “below”. Just regarding what? For getting complete information about the position of a point on the physical surface of the Earth, the third coordinate is used - height . Therefore, there is a need to consider the third coordinate system - height system .

The distance along a plumb line from a level surface to a point on the physical surface of the Earth is called height.

There are heights absolute , if they are counted from the level surface of the Earth, and relative (conditional ), if they are counted from an arbitrary level surface. Typically, the starting point for absolute heights is taken to be the level of the ocean or open sea at calm state. In Russia and Ukraine, the starting point for absolute altitude is taken to be zero of the Kronstadt footstock.

Footstock- a rail with divisions, fixed vertically on the shore so that it is possible to determine from it the position of the water surface in a calm state.
Kronstadt footstock- a line on a copper plate (board) mounted in the granite abutment of the Blue Bridge of the Obvodny Canal in Kronstadt.
The first footpole was installed during the reign of Peter 1, and from 1703 regular observations of the level of the Baltic Sea began. Soon the footstock was destroyed, and only from 1825 (and to the present) regular observations were resumed. In 1840, hydrographer M.F. Reinecke calculated the average height of the Baltic Sea level and recorded it on the granite abutment of the bridge in the form of a deep horizontal line. Since 1872, this line has been taken as the zero mark when calculating the heights of all points on the territory of the Russian state. The Kronstadt footing rod was modified several times, but the position of its main mark was kept the same during design changes, i.e. defined in 1840
After the breakup Soviet Union Ukrainian surveyors did not invent their own national system heights, and is currently still used in Ukraine Baltic height system.

It should be noted that in each if necessary do not measure directly from the level of the Baltic Sea. There are special points on the ground, the heights of which were previously determined in the Baltic height system. These points are called benchmarks .
Absolute altitudes H can be positive (for points above the Baltic Sea level), and negative (for points below the Baltic Sea level).
The difference in absolute heights of two points is called relative height or exceeding (h):
h =H A−H IN .
The excess of one point over another can also be positive or negative. If the absolute height of a point A greater than the absolute height of the point IN, i.e. is above the point IN, then the point is exceeded A above the point IN will be positive, and vice versa, exceeding the point IN above the point A- negative.

Example. Absolute heights of points A And IN: N A = +124,78 m; N IN = +87,45 m. Find mutual excesses of points A And IN.

Solution. Exceeding point A above the point IN
h A(B) = +124,78 - (+87,45) = +37,33 m.
Exceeding point IN above the point A
h B(A) = +87,45 - (+124,78) = -37,33 m.

Example. Absolute point height A equal to N A = +124,78 m. Exceeding point WITH above the point A equals h C(A) = -165,06 m. Find the absolute height of a point WITH.

Solution. Absolute point height WITH equal to
N WITH = N A + h C(A) = +124,78 + (-165,06) = - 40,28 m.

The numerical value of the height is called the point elevation (absolute or conditional).
For example, N A = 528.752 m - absolute point elevation A; N" IN = 28.752 m - reference point elevation IN .

Rice. 3.12. Heights of points on the earth's surface

To transition from conditional heights to absolute ones and vice versa, it is necessary to know the distance from the main level surface to the conditional one.

Video
Meridians, parallels, latitudes and longitudes
Determining the position of points on the earth's surface

Questions and tasks for self-control

1. Expand the concepts: pole, equatorial plane, equator, meridian plane, meridian, parallel, degree grid, coordinates.
2. Relative to what planes on the globe (ellipsoid of revolution) are geographic coordinates determined?
3. What is the difference between astronomical geographic coordinates and geodetic ones?
4. Using a drawing, explain the concepts of “spherical latitude” and “spherical longitude”.
5. On what surface is the position of points in the astronomical coordinate system determined?
6. Using a drawing, explain the concepts of “astronomical latitude” and “astronomical longitude”.
7. On what surface are the positions of points determined in a geodetic coordinate system?
8. Using a drawing, explain the concepts of “geodetic latitude” and “geodetic longitude”.
9. Why, to increase the accuracy of determining longitude, is it necessary to connect the ten-second divisions of the same name closest to the point with straight lines?
10. How can you calculate the latitude of a point by determining the number of minutes and seconds from the northern frame of a topographic map?
11. What coordinates are called polar?
12. What purpose does the polar axis serve in a polar coordinate system?
13. What coordinates are called bipolar?
14. What is the essence of the direct geodetic problem?

Counted from 0° to 90° on both sides of the equator. The geographic latitude of points lying in the northern hemisphere (northern latitude) is usually considered positive, the latitude of points in the southern hemisphere is considered negative. It is customary to speak of latitudes close to the poles as high, and about those close to the equator - as about low.

Due to the difference in the shape of the Earth from a sphere, the geographic latitude of points differs somewhat from their geocentric latitude, that is, from the angle between the direction to a given point from the center of the Earth and the plane of the equator.

Longitude

Longitude- angle λ between the plane of the meridian passing through a given point and the plane of the initial prime meridian from which longitude is measured. Longitudes from 0° to 180° east of the prime meridian are called eastern, and to the west - western. Eastern longitudes are considered to be positive, western longitudes are considered negative.

Height

To completely determine the position of a point in three-dimensional space, a third coordinate is needed - height. The distance to the center of the planet is not used in geography: it is convenient only when describing very deep regions of the planet or, on the contrary, when calculating orbits in space.

Within the geographic envelope, the “height above sea level” is usually used, measured from the level of the “smoothed” surface - the geoid. Such a three-coordinate system turns out to be orthogonal, which simplifies a number of calculations. Altitude above sea level is also convenient because it is related to atmospheric pressure.

Distance from the earth's surface (up or down) is often used to describe a place, however Not serves coordinate

Geographic coordinate system

The main disadvantage in practical application GSK in navigation is the large angular velocity of this system at high latitudes, increasing to infinity at the pole. Therefore, instead of the GSK, a semi-free CS in azimuth is used.

Semi-free in azimuth coordinate system

The azimuth-semi-free CS differs from the GSK in only one equation, which has the form:

Accordingly, the system also has starting position that the GCS and their orientation also coincide with the only difference that its axes and are deviated from the corresponding axes of the GCS by an angle for which the equation is valid

The conversion between the GSK and the semi-free CS in azimuth is carried out according to the formula

In reality, all calculations are carried out in this system, and then, to produce output information, the coordinates are converted into the GSK.

Geographic coordinate recording formats

The WGS84 system is used to record geographic coordinates.

Coordinates (latitude from -90° to +90°, longitude from -180° to +180°) can be written:

• in ° degrees as a decimal (modern version)
• in ° degrees and "minutes with decimal fraction
• in ° degrees, "minutes and" seconds with decimal fraction (historical form of notation)

Separator decimal the point always serves. Positive coordinate signs are represented by a (in most cases omitted) "+" sign, or by the letters: "N" - north latitude and "E" - east longitude. Negative coordinate signs are represented either by a “-” sign or by the letters: “S” is south latitude and “W” is west longitude. Letters can be placed either in front or behind.

There are no uniform rules for recording coordinates.

Search engine maps by default show coordinates in degrees and decimals, with "-" signs for negative longitude. On Google maps and Yandex maps, latitude comes first, then longitude (until October 2012, the reverse order was adopted on Yandex maps: first longitude, then latitude). These coordinates are visible, for example, when plotting routes from arbitrary points. Other formats are also recognized when searching.

In navigators, by default, degrees and minutes with a decimal fraction with a letter designation are often shown, for example, in Navitel, in iGO. You can enter coordinates in accordance with other formats. The degrees and minutes format is also recommended for maritime radio communications.

At the same time, the original method of recording with degrees, minutes and seconds is often used. Currently, coordinates can be written in one of many ways or duplicated in two main ways (with degrees and with degrees, minutes and seconds). As an example, options for recording the coordinates of the sign “Zero kilometer of highways of the Russian Federation” - 55.755831 , 37.617673 55°45′20.99″ n. w. /  55.755831 , 37.617673 37°37′03.62″ E. d.:

• (G) (O) (I)
• 55.755831°, 37.617673° -- degrees
• N55.755831°, E37.617673° -- degrees (+ additional letters)
• 55°45.35"N, 37°37.06"E -- degrees and minutes (+ additional letters)

55°45"20.9916"N, 37°37"3.6228"E -- degrees, minutes and seconds (+ additional letters)

• Links
• Geographic coordinates of all cities on Earth (English)
• Geographic coordinates of populated areas on Earth (1) (English)
• Geographic coordinates of populated areas on Earth (2) (English)
• Converting coordinates from degrees to degrees/minutes, to degrees/minutes/seconds and back

Converting coordinates from degrees to degrees/minutes/seconds and back

see also

Notes

Wikimedia Foundation.

2010. See what “Geographic coordinates” are in other dictionaries:

See Coordinates. Mountain encyclopedia. M.: Soviet Encyclopedia. Edited by E. A. Kozlovsky. 1984 1991 … Geological encyclopedia

- (latitude and longitude), determine the position of a point on the earth’s surface. Geographic latitude j is the angle between the plumb line at a given point and the plane of the equator, measured from 0 to 90 latitude on both sides of the equator. Geographical longitude l angle… … Modern encyclopedia

Latitude and longitude determine the position of a point on the earth's surface. Geographic latitude? the angle between the plumb line at a given point and the plane of the equator, measured from 0 to 90. in both directions from the equator. Geographic longitude? angle between... ...

Big Encyclopedic Dictionary

Latitude

Angular values ​​that determine the position of a point on the Earth’s surface: latitude – the angle between the plumb line at a given point and the plane of the earth’s equator, measured from 0 to 90° (north of the equator is northern latitude and south of southern latitude); longitude... ...Nautical Dictionary Similar coordinates are used on other planets, as well as on the celestial sphere. high, and about those close to the equator - as about low.

Due to the difference in the shape of the Earth from a sphere, the geographic latitude of points differs somewhat from their geocentric latitude, that is, from the angle between the direction to a given point from the center of the Earth and the plane of the equator.

The latitude of a place can be determined using astronomical instruments such as a sextant or gnomon (direct measurement), or you can use GPS or GLONASS systems (indirect measurement).

Video on the topic

Longitude

Longitude- dihedral angle λ between the plane of the meridian passing through a given point and the plane of the initial prime meridian from which longitude is measured. Longitude from 0° to 180° east of the prime meridian is called eastern, and to the west is called western. Eastern longitudes are considered to be positive, western longitudes are considered negative.

Height

To completely determine the position of a point in three-dimensional space, a third coordinate is needed - height. The distance to the center of the planet is not used in geography: it is convenient only when describing very deep regions of the planet or, on the contrary, when calculating orbits in space.

Within the geographical envelope it is usually used height above sea level, measured from the level of the “smoothed” surface - geoid. Such a three-coordinate system turns out to be orthogonal, which simplifies a number of calculations. Altitude above sea level is also convenient because it is related to atmospheric pressure.

Distance from the earth's surface (up or down) is often used to describe a place, but "not" serves as a coordinate.

Geographic coordinate system

ω E = − V N / R (\displaystyle \omega _(E)=-V_(N)/R) ω N = V E / R + U cos ⁡ (φ) (\displaystyle \omega _(N)=V_(E)/R+U\cos(\varphi)) ω U p = V E R t g (φ) + U sin ⁡ (φ) (\displaystyle \omega _(Up)=(\frac (V_(E))(R))tg(\varphi)+U\sin(\ varphi)) where R is the radius of the earth, U is the angular velocity of the earth's rotation, V N (\displaystyle V_(N))- speed vehicle on North, V E (\displaystyle V_(E))- to the East, φ (\displaystyle \varphi )- latitude, λ (\displaystyle \lambda)- longitude.

The main disadvantage in the practical application of G.S.K. in navigation is the large angular velocity of this system at high latitudes, increasing to infinity at the pole. Therefore, instead of G.S.K., semi-free in azimuth SK is used.

Semi-free in azimuth coordinate system

Semi-free in azimuth S.K. differs from G.S.K. only by one equation, which has the form:

ω U p = U sin ⁡ (φ) (\displaystyle \omega _(Up)=U\sin(\varphi))

Accordingly, the system also has an initial position, carried out according to the formula

N = Y w cos ⁡ (ε) + X w sin ⁡ (ε) (\displaystyle N=Y_(w)\cos(\varepsilon)+X_(w)\sin(\varepsilon)) E = − Y w sin ⁡ (ε) + X w cos ⁡ (ε) (\displaystyle E=-Y_(w)\sin(\varepsilon)+X_(w)\cos(\varepsilon))

In reality, all calculations are carried out in this system, and then, to produce output information, the coordinates are converted into the GSK.

Geographic coordinate recording formats

Any ellipsoid (or geoid) can be used to record geographic coordinates, but WGS 84 and Krasovsky (in the Russian Federation) are most often used.

Coordinates (latitude from −90° to +90°, longitude from −180° to +180°) can be written:

• in ° degrees as a decimal (modern version)
• in ° degrees and ′ minutes with decimal fraction
• in ° degrees, ′ minutes and

Sometimes you may need to accurately calculate the geographic coordinates of your location or some object, but you have nothing with you except a map. It is not difficult to learn how to determine latitude and longitude on a map; you just need to get a clear understanding of what the coordinate system is and how to work with it.

The coordinate system is a kind of geographic “registration” that any point on the planet has. A grid of meridians and parallels, applied on top of the canvas of any image of the area, helps determine the latitude and longitude of the desired object from the map. Let's look at how it can be used to search for a geographic location.

What is a coordinate system?

People invented a system that reads the coordinates of any point a long time ago. This system consists of parallels indicating latitude and meridians indicating longitude.

Since it was difficult to determine latitude and longitude by eye, a grid of longitudinal and transverse arcs, indicated by numbers, began to be applied over all types of geographical images.

What does latitude mean?

The number responsible for the latitude of a place on the map indicates its distance relative to the equator - the further the point is from it and the closer to the pole, the more its digital value increases.

• On flat images, as well as globes, latitude is determined by spherical lines drawn horizontally and parallel to the equator - parallels.
• At the equator there is a zero parallel, towards the poles the value in numbers increases.
• Parallel arcs are designated in degrees, minutes, seconds, as angular measurements.
• From the equator towards the north pole, the value will have positive values ​​from 0º to 90º, indicated by the symbols “n. latitude,” that is, “north latitude.”
• And from the equator towards the south - negative, from 0º to -90º, indicated by the symbols “southern latitude”, that is, “southern latitude”.
• The values ​​90º and -90º are at the peak of the poles.
• Latitudes close to the equator are called “low”, and those close to the poles are called “high”.

To determine the location of the required object relative to the equator, you just need to correlate its point with the nearest parallel, and then look at what number is opposite it to the left and right behind the map field.

• If the point is located between the lines, you must first determine the nearest parallel.
• If it is north of the desired point, then the coordinate of the point will be smaller, so from the nearest horizontal arc you need to subtract the difference in degrees to the object.
• If the nearest parallel is below the desired point, then the difference in degrees is added to its value, since the desired point will have a larger value.

Since it is sometimes difficult to determine latitude and longitude on a map at a glance, they use a ruler with a pencil or compass.

Remember! All points on the globe, and accordingly on a map or globe, located along one parallel arc will have the same value in degrees.

What does longitude mean?

Meridians are responsible for longitude - vertical spherical arcs converging at the poles into one point, dividing the globe into 2 hemispheres - western or eastern, which we are used to seeing on the map in the form of two circles.

• Meridians similarly facilitate the task of accurately determining the latitude and longitude of any point on earth, since the place of their intersection with each of the parallels is easily indicated by a digital mark.
• The value of vertical arcs is also measured in angular degrees, minutes, seconds, ranging from 0º to 180º.
• Starting from 1884, it was decided to take the Greenwich meridian as the zero mark.
• All coordinate values ​​in the direction west of Greenwich are designated by the symbol “W,” that is, “western longitude.”
• All values ​​in the direction east of Greenwich are designated by the symbol “E,” that is, “Eastern longitude.”
• All points located along the same meridian arc will have the same designation in degrees.

Remember! To calculate the longitude value, you need to correlate the location of the desired object with the digital designation of the nearest meridian, which is placed outside the image fields above and below.

How to find the coordinates of the desired point

The question often arises of how to determine latitude and longitude on a map if the desired point, distant from the coordinate grid, is located inside a square.

Calculating coordinates is also difficult when the image of the area is on a huge scale, and you don’t have more detailed information with you.

• Here you cannot do without special calculations - you will need a ruler with a pencil or a compass.
• First, the nearest parallel and meridian are determined.
• Their digital designation is recorded, then the step.
• Next, the distance from each of the arcs is measured in millimeters, then converted to kilometers using a scale.
• All this correlates with the pitch of parallels, as well as the pitch of meridians drawn on a certain scale.
• There are images with different pitches - 15º, 10º, and there are less than 4º, this directly depends on the scale.
• Having found out the distance between the nearest arcs, also the value in degrees, you need to calculate the difference, by how many degrees a given point is deviated from the coordinate grid.
• Parallel - if the object is in the northern hemisphere, then we add the resulting difference to the smaller number, and subtract it from the larger one; for the southern hemisphere, this rule works similarly, only we carry out the calculations as with positive numbers, but the final number will be negative.
• Meridian - the position of a given point in the eastern or western hemisphere does not affect the calculations; we add our calculations to the smaller value of the parallel, and subtract from the larger value.

Using a compass is also easy to calculate the geographic location - to get the value of the parallel, its ends need to be placed on the point of the desired object and the nearest horizontal arc, and then the thrust of the compass must be transferred to the scale of the existing map. And to find out the size of the meridian, repeat all this with the nearest vertical arc.

On globes and geographical maps there is a coordinate system. With its help, you can plot any object on a globe or map, as well as find it on the earth's surface. What is this system, and how to determine the coordinates of any object on the surface of the Earth with its participation? We will try to talk about this in this article.

Geographic latitude and longitude

Longitude and latitude – geographical concepts, which are measured in angular units (degrees). They serve to indicate the position of any point (object) on the earth's surface.

Geographic latitude is the angle between a plumb line at a particular point and the plane of the equator (zero parallel). Latitude in the Southern Hemisphere is called southern, and in the Northern Hemisphere it is called northern. Can vary from 0∗ to 90∗.

Geographic longitude is the angle made by the meridian plane at a certain point to the plane of the prime meridian. If the longitude is counted east from the prime Greenwich meridian, then it will be east longitude, and if it is to the west, then it will be west longitude. Longitude values ​​can range from 0∗ to 180∗. Most often, on globes and maps, meridians (longitude) are indicated when they intersect with the equator.

How to determine your coordinates

If a person gets into emergency he must, first of all, be well versed in the terrain. In some cases, it is necessary to have certain skills in determining the geographic coordinates of your location, for example, in order to convey them to rescuers. There are several ways to do this using improvised methods. We present the simplest of them.

Determining longitude by gnomon

If you go traveling, it is best to set your watch to Greenwich time:

• It is necessary to determine when it will be noon GMT in a given area.
• Insert a stick (gnomon) to determine the shortest solar shadow at noon.
• Find the minimum shadow cast by the gnomon. This time will be local noon. In addition, this shadow will point strictly north at this time.
• Using this time, calculate the longitude of the place where you are.

Calculations are made based on the following:

• since the Earth makes a complete revolution in 24 hours, therefore, it will travel 15 ∗ (degrees) in 1 hour;
• 4 minutes of time will be equal to 1 geographical degree;
• 1 second of longitude will be equal to 4 seconds of time;
• if noon occurs before 12 o'clock GMT, this means that you are in the Eastern Hemisphere;
• If you spot the shortest shadow after 12 o'clock GMT, then you are in the Western Hemisphere.

An example of the simplest calculation of longitude: the shortest shadow was cast by the gnomon at 11 hours 36 minutes, that is, noon came 24 minutes earlier than at Greenwich. Based on the fact that 4 minutes of time are equal to 1 ∗ longitude, we calculate - 24 minutes / 4 minutes = 6 ∗. This means that you are in the Eastern Hemisphere at 6 ∗ longitude.

How to determine geographic latitude

The determination is made using a protractor and a plumb line. To do this, a protractor is made from 2 rectangular strips and fastened in the form of a compass so that the angle between them can be changed.

• A thread with a load is fixed in the central part of the protractor and plays the role of a plumb line.
• With its base, the protractor is aimed at the North Star.
• 90 ∗ is subtracted from the angle between the plumb line of the protractor and its base. The result is the angle between the horizon and the North Star. Since this star is only 1 ∗ deviated from the axis of the world pole, the resulting angle will be equal to the latitude of the place where you are currently located.

How to determine geographic coordinates

The simplest way to determine geographic coordinates, which does not require any calculations, is this:

• Google maps opens.
• Find the exact place there;
  • the map is moved with the mouse, moved away and zoomed in using its wheel
  • find a settlement by name using the search.
• Right-click on the desired location. Select from the menu that opens required item. In this case, “What is here?” Geographic coordinates will appear in the search line at the top of the window. For example: Sochi - 43.596306, 39.7229. They indicate the geographic latitude and longitude of the center of that city. This way you can determine the coordinates of your street or house.

Using the same coordinates you can see the place on the map. You just can’t swap these numbers. If you put longitude first and latitude second, you risk ending up in a different place. For example, instead of Moscow you will end up in Turkmenistan.

How to determine coordinates on a map

To determine the geographic latitude of an object, you need to find the closest parallel to it from the equator. For example, Moscow is located between the 50th and 60th parallels. The closest parallel from the equator is the 50th. To this figure is added the number of degrees of the meridian arc that is calculated from the 50th parallel to the desired object. This number is 6. Therefore, 50 + 6 = 56. Moscow lies on the 56th parallel.

To determine the geographic longitude of an object, find the meridian where it is located. For example, St. Petersburg lies east of Greenwich. Meridian, this one is 30 ∗ away from the prime meridian. This means that the city of St. Petersburg is located in the Eastern Hemisphere at a longitude of 30 ∗.

How to determine the coordinates of the geographic longitude of the desired object if it is located between two meridians? At the very beginning, the longitude of the meridian that is located closer to Greenwich is determined. Then to given value it is necessary to add the number of degrees that is on the parallel arc the distance between the object and the meridian closest to Greenwich.

Example, Moscow is located east of the 30 ∗ meridian. Between it and Moscow the arc of parallel is 8 ∗. This means that Moscow has an eastern longitude and it is equal to 38 ∗ (E).

How to determine your coordinates on topographic maps? Geodetic and astronomical coordinates of the same objects differ on average by 70 m. Parallels and meridians on topographic maps are the inner frames of the sheets. Their latitude and longitude are written in the corner of each sheet. Western Hemisphere map sheets are marked "West of Greenwich" in the northwest corner of the frame. Maps of the Eastern Hemisphere will accordingly be marked “East of Greenwich.”