Geographic longitude and latitude are used to accurately determine the physical location of any object on the globe. The easiest way to find geographic coordinates is to use a geographic map. This method requires some theoretical knowledge for its implementation. How to determine longitude and latitude is described in the article.
Geographical coordinates
Coordinates in geography are a system in which each point on the surface of our planet is assigned a set of numbers and symbols that allows you to accurately determine the position of this point. Geographic coordinates are expressed in three numbers - this is latitude, longitude and altitude. The first two coordinates, that is, latitude and longitude, are most often used in various geographical tasks. The beginning of the report in the geographical coordinate system is in the center of the Earth. To represent latitude and longitude, spherical coordinates are used, which are expressed in degrees.
Before considering the question of how to determine longitude and latitude by geography, you should understand these concepts in more detail.
Concept of latitude
The latitude of a specific point on the Earth's surface is the angle between the equatorial plane and the line connecting this point with the center of the Earth. Through all the points on the surface of the earth having the same latitude, you can draw a plane that will be parallel to the plane of the equator.
The equatorial plane is the zero parallel, that is, its latitude is 0 °, and it divides the entire globe into the southern and northern hemispheres. Accordingly, the north pole lies parallel to 90 ° north latitude, and the south pole lies parallel to 90 ° south latitude. The distance, which corresponds to 1 ° when moving along a particular parallel, depends on what kind of parallel it is. With increasing latitude, moving north or south, this distance decreases. Thus, the longest parallel is 0 °. Knowing that the circumference of the Earth at the latitude of the equator has a length of 40,075.017 km, we obtain a length of 1 ° along this parallel equal to 111.319 km.
Latitude shows how far north or south from the equator this point lies on the surface of the Earth.
The concept of longitude
The longitude of a specific point on the Earth’s surface is the angle between the plane passing through this point and the axis of rotation of the Earth and the plane of the zero meridian. By settlement, the meridian is assumed to be zero, which passes through the Royal Observatory in Greenwich, located in the southeast in England. The Greenwich Meridian divides the globe into the eastern and western hemispheres.
Thus, each line of longitude passes through the north and south poles. The lengths of all meridians are equal and amount to 40007.161 km. If we compare this figure with the length of the zero parallel, we can say that the geometric shape of the planet Earth is a ball flattened from the poles.
Longitude shows how far to the west or east of the zero (Greenwich) meridian lies a specific point on the Earth. If the latitude has a maximum value of 90 ° (latitude of the poles), then the maximum value of longitude is 180 ° west or east of the prime meridian. The 180 ° Meridian is known as the International Date Line.
One may ask an interesting question, the longitude of which points cannot be determined. Based on the definition of the meridian, we get that through 360 points on the surface of our planet all 360 meridians pass, these points are the south and north poles.
Geographic degree
From the above figures it can be seen that 1 ° on the Earth's surface corresponds to a distance of more than 100 km, which is along the parallel, and along the meridian. For a more accurate determination of the geographical coordinates of the object, the degree is divided into tenths and hundredths, for example, they speak of 35.79 north latitude. In this form, information is provided by satellite navigation systems such as GPS.
Conventional geographical and topographic maps of a fraction of a degree are presented in the form of minutes and seconds. So, each degree is divided into 60 minutes (indicated by 60 '), and each minute is divided into 60 seconds (indicated by 60' '). Here you can draw an analogy with the representation of the measurement of time.
Acquaintance with a geographical map
To understand how to determine the geographical latitude and longitude on a map, you must first familiarize yourself with it. In particular, you need to understand how the coordinates of longitude and latitude are represented on it. First, the upper part of the map shows the northern hemisphere, the lower part - the southern one. The numbers that are on the left and right on the edge of the map indicate latitude, and the numbers located at the top and bottom of the map indicate longitude coordinates.
Before determining the coordinates of latitude and longitude, you must remember that they are presented on the map in degrees, minutes and seconds. This system of units should not be confused with decimal fractions of a degree. For example, 15 '= 0.25 °, 30' = 0.5 °, 45 '' = 0.75 '.
Using a geographical map to determine longitude and latitude
We will explain in detail how to determine longitude and latitude by geography using a map. To do this, you first need to purchase a standard geographic map. This map may be a map of a small area, region, country, continent or the whole world. To understand which card to deal with, you should read its name. Below, under the name, the limits of latitudes and longitudes can be given, which are presented on the map.
After that, you need to select some point on the map, some object that you want to mark in some way, for example, with a pencil. How to determine the longitude of an object located at a selected point, and how to determine its latitude? The first step is to find the vertical and horizontal lines that lie closest to the selected point. These lines are the latitude and longitude, the numerical values of which can be viewed at the edges of the map. Assume that the selected point lies between 10 ° and 11 ° north latitude and 67 ° and 68 ° west longitude.
Thus, we know how to determine the geographical latitude and longitude of the object selected on the map with the accuracy that the map provides. In this case, the accuracy is 0.5 °, both in latitude and in longitude.
Determining the exact value of geographical coordinates
How to determine the longitude and latitude of a point more accurately than 0.5 °? First you need to find out what scale the map with which the work is conducted has. Usually, a scale ruler is indicated in one of the corners of the map, showing the correspondence of distances on the map to distances in geographical coordinates and in kilometers on the ground.
After the scale ruler is found, you need to take a simple ruler with millimeter divisions and measure the distance on the scale ruler. Suppose that in this example, 50 mm corresponds to 1 ° of latitude and 40 mm to 1 ° of longitude.
Now we position the ruler so that it is parallel to the lines of longitude drawn on the map and measure the distance from the point in question to one of the nearest parallels, for example, the distance to the 11 ° parallel is 35 mm. We compose a simple proportion and we get that this distance corresponds to 0.3 ° from the parallel 10 °. Thus, the latitude of the considered point is + 10.3 ° (plus sign means north latitude).
Similar actions should be done for longitude. To do this, place the ruler parallel to the lines of latitude and measure the distance to the nearest meridian from the selected point on the map, for example, this distance is 10 mm to the meridian 67 ° west longitude. According to the rules of proportion, we get that the longitude of the object in question is -67.25 ° (minus sign means west longitude).
Translation of degrees in minutes and seconds
As mentioned above, 1 ° = 60 '= 3600' '. Using this information and the proportion rule, we get that 10.3 ° corresponds to 10 ° 18'0 ''. For the value of longitude we get: 67.25 ° = 67 ° 15'0``. In this case, the translation used the proportion once for longitude and latitude. However, in the general case, when fractional minutes are obtained once after using the proportion, you should use the proportion a second time to get the value of the extra seconds. Note that the accuracy of determining coordinates to 1 'corresponds to accuracy on the surface of the globe, equal to 30 meters.
Record of received coordinates
After the question of how to determine the longitude of the object and its latitude is sorted out and the coordinates of the selected point are determined, they should be correctly written. The standard form of recording implies the indication of longitude after latitude. Both values must be indicated with as many decimal places as possible, since the accuracy of the location of the object depends on this.
Certain coordinates can be represented in two different formats:
- Using only the degree icon, for example, + 10.3 °, -67.25 °.
- Using minutes and seconds, for example, 10 ° 18'0 '' north latitude, 67 ° 15'0 '' west longitude.
It should be noted that in the case of representing geographical coordinates using degrees only, the words "north (south) latitude" and "east (west) longitude" are replaced with the corresponding plus or minus signs.