by the late 1800s, due largely to Great Britain’s maritime dominance in the nineteenth century, most maps began using the prime meridian at Greenwich, England.
Latitude and longitude coordinates can be written in decimal or degree/minutes/seconds formats (figure 1.18). For example, the White House, located between the 38th and 39th northern parallels and between the 77th and 78th western meridians, is written as follows:
Decimal degrees: 38.8977° N, 77.0366° W
Degrees/minutes/seconds: N 38° 53' 49.5456”, W 77° 2' 11.562”
Another commonly used method for describing the location of a place is with street addresses, whereby each address refers to a specific building in a specific place. The location for the White House, as a street address, is 1600 Pennsylvania Ave NW, Washington, DC 20500.
One unusual and innovative coordinate system has been developed by What-3-Words. With this coordinate system, the entire world is divided into 3 × 3 meter grids, each of which is assigned three words. Thus, every place on the earth’s surface can be identified with just three words within three meters of accuracy. This has some advantages compared to traditional coordinate systems. First, many places do not have an official street address, which severely restricts the usefulness of a street address system in identifying locations. Second, while latitude and longitude describe specific locations, they are too long and complicated for most people to remember. In contrast, it is quite easy to remember three words. With this system, the location of the White House is described as “sulk.held.raves.” With the What-3-Words app, businesses and governments can deliver goods and services to precise locations, from the proper building entrance on a large corporate campus to a remote home in rural Kenya. In 2016, the postal service of Mongolia, where few streets have official names, began using this system nationwide.
Many other types of coordinate systems are used throughout the world. When you take additional classes on geography and geographic information systems, you will be able to delve more deeply into them.
Counts vs. rates
Another issue to keep in mind when creating and reading maps is the difference between counts and rates. As the name implies, counts are a count of the number of features in an area. A population count map will show the number of people in an area, such as a city, while a terrorist activity count map will show the number of terrorist incidents, such as within a country.
Figure 1.18.Latitude and longitude: Location of the White House. This map shows the location of the White House in relation to 1-degree latitude and longitude grid lines. Explore this map at http://arcg.is/2m4WPKR. Map by author. Data sources: Esri, HERE, Garmin, NGA, USGS, NPS.
Rates compare one variable to another. In geography, it is common to calculate rates on the basis of population or area. A wheat production map can show the amount of wheat within a county divided by the area in square miles of the county, resulting in wheat production per square mile. Likewise, the number of people with influenza within a state can be divided by the total population of the state, giving the influenza rate per 100,000 people.
Understanding the difference between counts and rates is essential. If a political party targets the Hispanic community and is looking for a good location for a get-out-the-vote campaign, a map showing counts and a map showing rates can lead to very different location decisions (figure 1.19). For instance, there may be census tracts with a very high proportion of Hispanic people (i.e., a high rate). This high rate may appear to indicate a good location for the campaign. However, while 90 percent of the population may be Hispanic, when mapping counts, it may turn out that there are only 100 people in the census tract. The small number of people may make the census tract a poor location in reality.
Figure 1.19.Counts vs. rates. When creating and interpreting maps, very different impressions result from classifying data by rates and by counts. Explore these maps at https://arcg.is/0H1uvO. Maps by author. Data sources: 2016 USA Diversity Index. Esri, US Census Bureau.
Map classification
The classification scheme used with a map can have a major impact on the way it is interpreted. With a choropleth map, data is divided into categories, and then each category is given a color or shade. But the number of categories and the cutoff points for each category can dramatically alter the look of a map (figure 1.20). In the following example, a map using equal interval classification would show incomes of $160,000 in the top category. However, the quantile classification scheme would include all households earning $79,894 or more. Obviously, the map looks very different depending solely on the chosen classification scheme (figure 1.21). One scheme gives the impression that wide swaths of the Seattle region are upper income, while the other scheme makes the prevalence of upper income areas look much more limited.
Note that changing the map classification scheme does not involve changing any of the data. The data remains exactly the same. All that changes are the cutoff points for each color category. Cartographers can thus easily manipulate the perception that a map gives without falsifying data in any way.
Go to ArcGIS Online to complete exercise 1.2: “Map basics with ArcGIS Online.”
The geographic perspective
As discussed at the beginning of this chapter, geography is a discipline that, at its core, asks where things are located and why they are there. Broadly speaking, geography can be seen from a spatial perspective and an ecological perspective. The spatial perspective examines spatial distributions and processes, while the ecological perspective offers a holistic view that incorporates both human actions and environmental opportunities and constraints. This section dives deeper into the fundamental concepts that constitute the geographic perspective.
Figure 1.20.Classification schemes. Different classification schemes using the USA Median Household Income layer. Note how the category cutoff points can change dramatically depending on the classification scheme used. Image by author. Data Source: Esri, US Census Bureau.
Figure 1.21.Classification schemes: Quantile vs. equal interval. One classification scheme gives the impression that most of Seattle is affluent, while the other shows affluent areas as much more limited in scope. Explore this map at http://arcg.is/2m5n4B3. Maps by author. Data sources: 2016 USA Median Household Income by Esri; Esri, US Census Bureau.
Space
Location and distance are key components of geographic inquiry and can be viewed in both absolute and relative terms.
Absolute location describes a fixed point on the surface of the earth. The latitude and longitude coordinate systems, as well as street address systems, refer to absolute location.
Relative location is another way of describing where things are and is arguably more significant for much geographic research. Relative location describes where a feature is located in relation to another feature. For example, the location of a house can be described as 1 mile from the freeway, close to shopping, far from the beach, or adjacent to a park. Each of these terms describes where the house is located relative to other important landscape
