Latitude and longitude are measurements of location on the globe. If you can read latitude and longitude on a map, you can determine the geographic coordinates of any place on it. While online maps provide latitude and longitude data with the click of a button, knowing how to do it on paper is often helpful. To read latitude and longitude correctly, you first have to understand the basics of these measurements. When you have mastered the essentials, you will learn to identify latitude and longitude markers on a map and to locate exact locations.
Method 1 of 2: Understand Latitude and Longitude
Step 1. Familiarize yourself with the concept of latitude
Latitude is a measure of distance north or south of the equator, consisting of an imaginary horizontal line around the exact midpoint of the Earth between the 2 poles. The Earth is divided into 180 lines of latitude on each side of the equator called parallels. The parallels are distributed horizontally around the Earth, parallel to the equator: 90 of them north of the equator and the remaining 90, south of this.
Step 2. Learn the definition of longitude
Longitude is a measure of distance to the east or west of an imaginary vertical line that runs through the center of the globe from the North Pole to the South Pole, called the prime meridian. Lines of longitude are a series of vertical lines parallel to the prime meridian, also called meridians. There are 360 meridians on each side of the prime meridian, with 180 located east of the prime meridian and the remaining 180 to the west.
The meridian on the opposite side of the Earth from the prime meridian is called the antimeridian
Step 3. Study the units of measurement used for latitude and longitude
Latitude and longitude measurements are usually expressed in degrees (°), minutes (′), or seconds (″). The complete distance from one parallel or meridian to another is 1 °. For even more precise measurements, each degree can be further divided into 60 minutes and each minute into 60 seconds (for a total of 3,600 seconds per degree).
Latitude and longitude are measured in degrees rather than absolute units of measurement (such as miles or kilometers) because Earth is spherical. While the distance between degrees of latitude is constant (60 nautical miles or 111.12 km), the shape of the Earth causes the distance between degrees of longitude to decrease as you get closer to the poles
Step 4. Measure the latitude and longitude relative to point 0
When measuring latitude in any direction, the equator is considered the starting point, at latitude 0 °. In the same way, the prime meridian is the starting point for longitude measurements and represents 0 ° longitude. Any measure of latitude or longitude is expressed in terms of the distance from the point of origin in any direction.
- For example, the North Pole is at 90 ° N, which means it is 90 ° north of the equator.
- The antimeridian is 180 ° both east and west of the prime meridian.
- The Great Sphinx of Giza, in Egypt, is located at 29 ° 58′31 ″ N, 31 ° 8′15 ″ E. This means that it is located just below 30 ° north of the equator of latitude and about 31 ° to the east of the prime meridian of longitude.
Method 2 of 2: Determine latitude and longitude coordinates on a map
Step 1. Find a map with latitude and longitude lines
Not all maps show latitude and longitude. You are more likely to find them on large maps, such as atlas maps, or on smaller maps designed to reflect the terrain very accurately, such as topographic maps. If you are in the US, you can find detailed topographic maps of most regions through the US Geological Survey.
Step 2. Locate the location in which you are interested
Take a look at the map and locate the item or area for which you would like to know the coordinates. Mark the exact place you are interested in with a pin or pencil.
Step 3. Locate the latitude and longitude markers
Latitude is indicated on a map by a series of evenly spaced horizontal lines running from one side of the map to the other, while longitude is indicated by a series of evenly spaced vertical lines, running from top to bottom. down. Look for the numbers along the edges of the map that represent the coordinates of each line and are called "grids."
- Latitude grids are marked along the eastern and western edges of the map. Instead, the longitude grids are marked on the north and south edges.
- Depending on the scale of your map, the grids may mark fractions of degrees rather than full degrees. For example, there might be a grid marked every minute of a degree instead of every degree (eg, 32 ° 0 ′, 32 ° 1 ′, and so on).
- In addition, the map should also indicate where the displayed latitude and longitude are relative to the equator and the prime meridian respectively (eg, north or south, east or west).
- Be careful not to confuse latitude and longitude lines with UTM lines, another type of grid coordinate system that appears frequently on maps. UTM numbers are usually marked in smaller text (and without degree symbols) along the edges of the map, and UTM grids can be marked in a different color than latitude and longitude lines.
Step 4. Use a ruler to mark the latitude of your point
Using a ruler and pencil, mark a line horizontally from your point to the nearest eastern or western edge of the map. Make sure the line is parallel to the closest latitude line on the map.
Step 5. Draw another line to mark the length of the map
Starting from the same point, use the ruler and pencil to draw a straight vertical line to the nearest north or south edge of the map. Make sure the line is parallel to the closest line of longitude.
Step 6. Calculate the latitude and longitude of your point using the grids
Depending on the scale of the map, you can calculate the coordinates of your point up to the second. Observe where the latitude and longitude lines intersect with the coordinate lines at the edge of the map, and calculate the coordinates by their position relative to the nearest grids.
- If your map shows seconds, find the second closest to where each line intersects the latitude or longitude scale at the edge of the map. For example, if your latitude line falls about 5 ″ above the line 32 ° 20 ′ N, your point will be at a latitude of approximately 32 ° 20′5 ″ N.
- If the map shows minutes, but not seconds, you can calculate latitude or longitude in 6 seconds by dividing the space between each grid in tenths. If the line of longitude falls about 2/10 to the left of the line 120 ° 14 ′ E, the longitude is approximately 120 ° 14′12 ″ E.
Step 7. Join the measurements to determine the coordinates
Geographic coordinates represent where latitude and longitude lines converge at a single point. Review the numbers you got for the latitude and longitude of your point and join them together (eg, 32 ° 20′5 ″ N, 120 ° 14′12 ″ E).