1.3: Longitude and Latitude

Fourth Tool: Longitude and Latitude

To identify the locations of different climate phenomena, we need a coordinate system. While this may sound a bit intimidating, the fact is that you already use coordinate systems in your everyday life. Assume you didn't have access to Google Maps (or your GPS of choice). If you had to explain where you lived, you would probably use the intersection of two major streets/highways. For example, when people ask where De Anza is located, the answer is typically "Stevens Creek and CA-85" because those are the two most well-known highways. The intersection of those two main highways is a coordinate. You are also likely familiar with coordinates because you've likely used them at one point in a math class. Thankfully, the coordinate system of latitude and longitude that Meteorologists, Pilots, Geographers, Biologists, your GPS, and many others use is very similar to the X-Y coordinate system in your math classes. And plotting points on a map is just as easy as plotting points on an X-Y graph. Figure \(\PageIndex{1}\) shows how the globe is gridded into a coordinate system:

Figure \(\PageIndex{1}\): Longitude lines run from 0°-180°W or E of the Prime Meridian. 180°W/E of the Prime Meridian is called the International Date Line. It's exactly 180° (on the other side of) the Prime Meridian. Latitude Lines run from 0°-90° North or South of the Equator. 90°N is the North Pole, and 90°S is the South Pole. (Public Domain; Djexplo via Wikimedia Commons).

There are two coordinates that you need to identify a location:

• Longitude: The distance east (to the right of) or west (to the left of) the Prime Meridian, a line that runs from the North Pole, through Greenwich, England, and then to the South Pole.
• Latitude: The distance north (above) or south (below) of the Equator. Latitude lines run from 0°-90° North or South of the Equator. 90°N is the North Pole, and 90°S is the South Pole.

Put together, a latitude-longitude map of Earth looks like Figure \(\PageIndex{2}\).

Figure \(\PageIndex{2}\): World Map with lines of latitude and longitude. (CC-BY-NC-SA 4.0; Johnson et al. via Introduction to Historical Geology). Alternative description of image.

And to identify a point on this map, you simply start at 0° Longitude and 0° Latitude, and then travel to the appropriate longitude... and then move up to the appropriate latitude. For Example, 45°N, 45°E would look like the location starred on \(\PageIndex{3}\)

Figure \(\PageIndex{3}\): World Map with lines of Longitude and Latitude, and longitude 45°N/latitude 45°E starred. (CC-BY-NC-SA 4.0; Johnson et al. via Introduction to Historical Geology). Alternative description of image.

And 35°S, 120°W would look like the location starred on Figure 1.3.4:

Figure \(\PageIndex{4}\): World Map with lines of Longitude and Latitude, and longitude 35°S/latitude 120°W starred. (CC-BY-NC-SA 4.0; Johnson et al. via Introduction to Historical Geology). Alternative description of image.

Remember, Figures \(\PageIndex{2}\) through \(\PageIndex{4}\) are oriented with North on the top, South on the bottom, East on the right, West on the left. Based on this, let's answer the following questions.

6. Traveling South-to-North, the latitude North of the Equator (0°N/S) __________________________.
   1. Increases
   2. Decreases
7. Therefore, if you are traveling North in the United States, you are getting _________________________ from the Equator (0°N/S).
   1. Closer
   2. Further
8. Traveling West-to-East (left to right), the longitude West of the Prime Meridian _____________________ (the 0° Longitude line).
   1. Increases
   2. Decreases
9. Therefore, if you are traveling East in the United States you are getting _______________________ from the Prime Meridian (0°E/W).
   1. Closer
   2. Further
10. Which of the following places (labeled on the map) is located at 45°N (Lat), 105°W (Lon)
    1. A
    2. E
    3. I
    4. L
11. H is located at which lat/lon coordinate?
    1. 30°N, 90°W
    2. 60°N, 120°E
    3. 30°S, 30°E
    4. 15°S, 60°W

One major “trick” about the coordinate system comes from the fact that the Earth is a sphere rather than a flat surface. So quickly ask yourself… what happens if you start at the Prime Meridian and keep going west on a map of the world? Obviously, you don’t fall off the edge of the map, but what does happen? Try it with a globe… what happens then? The answer is that you end up all the way on the other side of the map! At some point, you’ve traveled so far west that you are now closer to the Prime Meridian from the East side (and therefore have an Eastern Longitude). A great example of this can be seen in a map of the Equatorial Pacific Ocean, such as Figure \(\PageIndex{5}\).

Figure \(\PageIndex{5}\): Sea-surface temperatures and anomalies for December 2015. (Public Domain; Monthly mean SST and Winds via NOAA/PMEL). Alternative description of image.

We use these maps to indicate the presence of a phenomenon called El Niño (we’ll cover that in a future investigation), but for now, let’s just focus on the coordinates. Again, the rule given earlier is still true. North is at the top, South at the bottom, West on the left, East on the right!

12. The eastern (right) side of this map is located in the ____________ hemisphere and therefore has a ________________ longitude coordinate.
    1. Eastern, West
    2. Eastern, East
    3. Western, West
    4. Western, East
13. The western (left) side of the map is located in the _____________ hemisphere and therefore has a _______________ longitude coordinate.
    1. Eastern, West
    2. Eastern, East
    3. Western, West
    4. Western, East

So what happened here? If you notice the 180° longitude line, everything to the left of it has an eastern coordinate while everything to the right has a western coordinate… that line is called the International Date Line… you can literally sail your way into tomorrow by crossing it because it is located exactly 180° (half way across the world) from the Prime Meridian and, since it’s almost entirely all ocean, few people are negatively impacted by switching a day as you travel across it. Pretty cool, huh?