2.2.1 Where are you right now?
The answer to the question will obviously depend on your location, but it will also depend on how you decide to describe where you are. Are you at home? If so, you may wish to describe your location with an address. Are you at school? If so, you would likely use the name of the building, such as the Science Library, to define where you are. Perhaps you are in a coffee shop, which would lead you to use the name of the place, such as the Marche Café. However, say you are filling out an online survey for a local retail store that would like to know the general vicinity in which you live. In such case, you would likely be asked to provide your postal or zip code that identifies the section of your city, town, or rural area where you reside. Finally, when creating your profile on a social networking site such as Facebook, you explain your location by entering the city and country where you are located, which are descriptors commonly referred to as place names.
As you can see, explaining where you are at any given moment depends on far more than just your location. Defining your location is influenced by who is asking you for information, your knowledge of where you are, how much detail is required, and how secure you feel with providing that information to others, especially when providing your location information on the web (for obvious reasons it is not suggested that we provide our exact addresses on social media sites). The rich variety of ways to describe our location is a good thing because we can explain where we are based on a specific purpose rather than providing one standard description for all intended purposes. For example, while providing an exact address may be useful when an online retailer needs to mail a package to your house, the same method is not useful if you are trying to tell a friend the coffee shop where you should meet. However, not having a standardized way to explain location can sometimes present a significant challenge.
The majority of people living on this planet have access to mobile phones. On every country on every continent, networks of cell towers exist in one form or another that are providing cellular access to an increasing range of individuals across social and economic classes. There are 196 countries in the world (although this number varies based on the organization providing this information) with nearly 7.2 billion people. Out of this population, the United Nations estimates that approximately 6 billion people (nearly 84%) have access to mobile phones. Given the thousands of languages spoken around the world and the rich history of hundreds of cultures that influence how we each describe our surroundings, how can billions of mobile phones across the globe describe to one another their location, and why is this even important? The answer to the first question is geographic coordinates. We will explore this and the answer to the second question in the sections below.
2.2.2 Geographic Coordinates
Geographic coordinates represent two numbers that explain your exact location on earth, numbers that are known as latitude and longitude. Type the following two numbers separated by a comma into the search box: “72.825833, 18.975”. Where does this take you? Where do you go if you type in “-43.196389, -22.908333”? How about “-21.933333, 64.133333”? From these examples can you understand how coordinates work?
Latitude represents your location relative to the equator, which is the line around the earth that divides the earth into the northern (above the equator) and southern (below the equator) hemisphere. You can see the equator in Map 2.2.1, and you can zoom in to see which countries fall above or below the equator, and which countries the equator intersects. Any location along the equator is represented by a latitude value of 0°. Locations above (north) of the equator are represented by values great than 0° up to 90° (the North Pole), while locations below (south) of the equator are represented by values less than 0° to -90° (the South Pole). You can see how this works by selecting Measure from the menu bar and then select the Location icon. Scroll your mouse away from the equator in either direction and you will see the value for latitude change accordingly.
Map 2.2.1
Longitude represents your location on the globe relative to a vertical line known as the prime meridian shown in Map 2.2.2 that divides the globe into two hemispheres. Locations along the prime meridian have a longitude of 0°, and locations to the right of the prime meridian have values from 0° to 180°, while locations to the left have values below 0° to -180°. Again, you can see how this works by selecting Measure from the menu bar and then select the Location icon. Scroll your mouse around the map to see how longitude changes as you move closer and further away from the prime meridian. But how was the location of the prime meridian chosen?
Map 2.2.2
The location of the equator is much easier to define because it represents the midway point between the north and south poles. However, what midpoint does the prime meridian serve? The answer is that it doesn’t. The prime meridian is an arbitrary line that runs through the Royal Observatory in Greenwich England. Many debates have taken place over centuries to determine where the prime meridian should be located, and while several prime meridians still exist today, the Greenwich meridian is the one on which the majority of geographic coordinate systems are based. See the story map below or click HERE to better understand the history of the prime meridian.
To summarize, we can define our location by geographic coordinates that are based on latitude and longitude. Values of latitude range from -90° at the South Pole to 90° at the North Pole with the equator representing 0°. Values of longitude extend to -180° as you move westward from the prime meridian and to 180° as you move eastward from the prime meridian. Looking at Map 2.2.3, what do you suppose your coordinates are? Make an educated guess, and then type your location in the search box. Click the Measure tool in the menu bar and select the Location icon. What do you suppose are the geographic coordinates of Mumbai? Rio de Janeiro? Kiev? Sydney? Vancouver? While you may find it difficult to estimate the exact location, by looking at the maps you should be able accurately state if these locations are north or south of the equator and west or east of the prime meridian. Therefore, you should be able to state if the coordinates have positive or negative values, thus knowing within what hemisphere these cities are located. Perform the same task that allowed you to find your coordinates in order to find the coordinates of these cities.
There are three important things to note about the values representing your geographic coordinates. First, coordinates are represented as degrees. In Map 2.2.3 you can mover your cursor around the map with the Location icon selected and see from the coordinates that the earth is dissected into 360° of longitude, 180° to the west and 180° to the east. In fact, sometimes you will see locations west of the prime meridian represented by a “W” rather than a negative symbol to indicate that it is to the west, and an “E” similarly represents locations to the east. The earth is also dissected by 180° of latitude, with 90° to the north and 90° to the south. Likewise, you will sometimes see the letters “N” and “S” to indicate north and south.
Map 2.2.3
Second, geographic coordinates contain a decimal point (.) followed by several numbers. Each number after the decimal increases the precision of the location. If you were only provided with the numbers to the left of the decimal point, you would only have a very vague idea of a specific location. For example, search for the location represented by latitude = 39° and longitude = 21° by typing in 39, 21 in the search box. If you zoom into this area you will see a purple box, which represents the general area that you are able to estimate location when providing coordinates with minimal precision. If you were provided with one number to the right of the decimal point, say 39.8, 21.4, your ability to determine a location would increase to precision defined by the red shaded box (enter these coordinates into the search box to see). However, only if you were provided with the full geographic coordinates 39.81667,21.41667°N, would you be able to understand that the location you are seeking is the city of Mecca in Saudi Arabia. (Note: ArcGIS Online requests coordinates in the form of longitude, latitude, while some other mapping applications may request coordinates in the form of latitude, longitude). As you can see, you can tell a mapping application the specific coordinates and you will be taken to the exact location. The more numbers you include after the decimal point, the more precise the application can be at providing the correct location.
Third, geographic coordinates can be represented in two ways. The first way is how we have been displaying coordinates thus far, which we refer to as decimal degrees. This is because our values contain a decimal point, and the value is represented in degrees as indicated by the degrees symbol at the end of the value. The other method is referred to as degrees, minutes, seconds, or the abbreviation DMS. The DMS system uses three values for both longitude and latitude: degree (°), minutes (‘), and seconds (“), hence the name DMS. Go back to the Measure window in map 2.2.3, and click on the Location icon and then click on the drop-down menu button next to Degrees. Here you can change the geographic coordinates to be represented as DMS. Now move the cursor around the map to see how the values of the coordinates change. Whether one uses decimal degrees or DMS is dependent on the purpose of the mapping application and the familiarity of the individual with either system. Both systems provide the same information but in different ways. DMS is slightly more complex to understand as it involves some elementary math to partition the globe. However, it works the same as DMS as providing values for minutes and seconds increases the precision of a location. Understanding how DMS works is something we leave up to more advanced materials on location, but the important thing here is to understand that it exists and that it operates similarly to decimal degrees.
2.2.3 The Use of Geographic Coordinates Systems in Society
As mentioned above, mobile devices such as cell phones and web-enabled tablets would not know each other’s location without a globally accepted standard for representing location. There are incredible examples of how location-enabled devices that utilize the geographic coordinate system have literally saved hundreds and thousands of lives in recent years (more on that soon). However, long before the days of smart phones and location-based technologies such as GPS receivers that tell us where to go when driving in our cars, geographic coordinate systems have been used to assist people in navigating across land, air and water. Can you think of any examples?
When we talk about location-enabled devices saving lives, perhaps nothing is more significant than the role of cell phones in the critical hours and days following natural disasters. On January 12, 2010, a catastrophic earthquake with a magnitude of 7.0 hit the country of Haiti, killing more than 100,00 people and destroying much of the country’s social and economic infrastructure. However, amazingly the majority of Haiti’s cellular tower network remained in tact, allowing individuals to call and text each other. This proved invaluable as an organization called Ushahidi (www.ushahidi.com) became involved and helped provide aid during the crisis. Ushahidi developed a crowdsourcing platform (more on that term later) that, in response to the earthquake, was able to determine the location of people in critical need of support. A text number, 4636, was created that people in need could contact and leave a message describing the severity of their situation. Texts were sent to a command center at Tufts University in Massachusetts where they were interpreted from Creole to English by volunteers. Since these messages were from cell phones that all had information on the geographic coordinates of the phone when the text was sent, volunteers could map the exact location of those in need and provide information in the map on the critical nature of their situation. A single map on the Web was created that included every person who texted 4636 for assistance, which was provided to aid workers on the ground in Haiti where they could provide food, water, and medical resources to ensure the safety of those affected by the earthquake. Location-based services relying on geographic coordinates were essential in this effort. See the story map below for more on this story and to better understand how knowledge of location saved thousands of lives.
We will visit other examples of how location-based services have served as an invaluable resource in disaster relief in future chapters, and we will continue to learn how location plays a vital role in many aspects of our lives and society as we progress through the remaining modules.