Latitude and longitude are used to indicate the position of a point on the earth's surface. If you know how to read them on a map, you can determine the geographic coordinates of any place. In many online maps it is possible to know the latitude and longitude of a place with one click, but sometimes it is useful to know how to do it on paper. To correctly read latitude and longitude, you must first understand the concepts behind these measurements. Once you have mastered the basics, learn how they are represented on a map and learn how to determine the exact location of a geographic point.
Steps
Part 1 of 2: Understanding the Concepts of Longitude and Latitude
Step 1. Familiarize yourself with the concept of latitude
Latitude measures the distance of a point, north or south, from the equator, that imaginary horizontal line that runs around the center of the Earth halfway between the two poles. The Earth is divided into 180 lines of latitude; these lines are called parallels and run horizontally on the earth's surface, parallel to the equator. 90 parallels are north of the equator, while the other 90 are south.
Step 2. Learn the definition of longitude
Longitude measures the distance of a point, east or west, from an imaginary line that runs vertically along the globe from the North Pole to the South Pole; this line is called the "fundamental meridian", "zero meridian" or "prime meridian", also known as the Greenwich meridian. The lines of longitude are a series of vertical lines parallel to the fundamental meridian, called meridians. There are 360 meridians, 180 of which lie to the east of the fundamental meridian and the other 180 to the west.
The meridian on the side of the globe opposite that of the fundamental meridian is called the antimeridian
Step 3. Consider the units used for latitude and longitude
Latitude and longitude are usually expressed in degrees (°), minutes (') and seconds ( ). The distance from one parallel or meridian to another is 1 °. For even more accurate measurements, each degree can be further divided into 60 minutes and each minute into 60 seconds (for a total of 3,600 seconds per grade).
Latitude and longitude are measured in degrees rather than absolute units (such as miles or kilometers) because the Earth is spherical. While the distance between the parallels is constant (60 nautical miles or 111.12 km), the shape of the Earth causes the distance between the meridians to decrease as you get closer to the Poles
Step 4. Measure latitude and longitude based on the point of origin
When measuring latitude in both directions (north or south), the equator is considered the point of origin, at a latitude of 0 °. Similarly, the fundamental meridian is the starting point for measuring longitude and corresponds to a longitude of 0 °. Latitude or longitude are always expressed in terms of angular distance and direction from the point of origin.
- For example, the North Pole is located at 90 ° N; this means it is 90 ° north of the equator.
- The antimeridian is located 180 ° east or west of the fundamental meridian.
- The Great Sphinx of Giza, Egypt is located at 29 ° 58 '31 "N, 31 ° 8' 15" E. This means that it is nearly 30 ° north of the equator in latitude and about 31 ° east of the fundamental meridian in longitude.
Part 2 of 2: Determining Latitude and Longitude on a Map
Step 1. Find a map showing latitude and longitude lines
Not all maps indicate latitude and longitude; they are more likely to be found on maps of large areas, such as those in atlases, or on maps of smaller territories designed to reflect the terrain extremely accurately, such as topographical ones. Many examples of Italian cartography are available on the IGM (Military Geographical Institute) website.
Step 2. Mark the location you are interested in on the map
Take a look at the map and locate the point or area whose coordinates you want to know. Mark the exact spot you are interested in with a push pin or pencil mark.
Step 3. Find the lines and latitude and longitude values
The latitude is indicated on the maps by a series of equidistant horizontal lines, the longitude by equidistant vertical lines; along the edges of the map there should be numbers indicating the values (degrees) of each line. This graphic representation constitutes the so-called "geographical grid".
- Latitude values are marked along the east and west edges of the map. Longitude values are marked on the north and south edges.
- Depending on the scale of the map, fractions of degrees may be indicated instead of full degrees. For example, there may be a grid that indicates every minute instead of every degree only (for example: 32 ° 0 ', 32 ° 1' and so on).
- The map should also indicate where the lines of latitude and longitude depicted lie with respect to the equator and the prime meridian (north or south, east or west).
- Be careful not to confuse lines of latitude and longitude with the UTM grid, another type of coordinate system often found on maps: the numbers are generally smaller and do not have the degree symbol and the lines can be of a different color from those of latitude and longitude.
Step 4. Use a ruler to mark the latitude of your point
Take a ruler and pencil and draw a horizontal line from the point of your choice to the closest edge of the map, left or right. Make sure your line is parallel to the nearest latitude line.
Step 5. Draw another line to mark the longitude
Starting at the same point, use the ruler and pencil to draw a vertical line to the nearest edge of the map, either bottom or top. Make sure your line is parallel to the closest longitude line.
Step 6. Calculate the latitude and longitude of your point using the grid
Depending on the scale of the map, you may be able to estimate the coordinates of your point down to the second. Observe where the latitude and longitude lines you drew intersect the values indicated on the edge of the map and make a rough estimate of the coordinates based on their position relative to the closest values.
- If your map shows seconds, find the second closest to where the line you drew touches the edge of the map. For example, if the latitude of your point is close to 5 "above the parallel 32 ° 20 'N, the point is at a latitude of approximately 32 ° 20' 5" N.
- If your map shows minutes, but not seconds, you can estimate latitude and longitude by dividing the space of each minute into ten small spaces of 6 seconds each. If the longitude line of your point is about 2/10 to the left of the 120 ° 14 'E meridian, the longitude is about 120 ° 14' 12 "E.
Step 7. Put your measurements together to determine the coordinates
The geographic coordinates correspond to the point on which the lines of latitude and longitude converge. Take the values you got for the latitude and longitude of your point and put them together (for example: 32 ° 20 '5 "N, 120 ° 14' 12" E).
