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 features.
By understanding the relative location of features, geographers can analyze how spatial relationships explain events. For instance, by knowing the relative location of countries in the Middle East and Europe, it is possible to understand migration flows out of war-torn Syria. Syrians will flee to nearby countries, such as Turkey, Lebanon, and Jordan, as well as to rich countries that are not too far away, such as Germany and Sweden. Many fewer migrants would be expected to go to farther away to Canada or the United States, which have a relative distance that is far from the Middle East.
As another example, relative location is useful in explaining real estate prices. Two identical houses, one adjacent to a golf course and one close to an industrial park, will have vastly different values, precisely because of their location relative to different land uses.
Closely related to location is the concept of distance. As with location, distance can be measured in absolute and relative terms. Absolute distance can be measured in traditional units, such as miles and feet or kilometers and meters. Relative distance looks at distance in terms of a surrogate value such as cost or difficulty.
Absolute distance is commonly measured by geographers in two ways (figure 1.22). Euclidean distance measures the distance between two points in a straight line. When people use the common vernacular “as the crow flies,” they are referring to Euclidean distance. Drawing a straight line from your house to school would give you the Euclidean distance. However, in peoples’ daily lives, they rarely travel in straight lines. For this reason, Manhattan distance, also called network distance, is also used in geographic analysis. Manhattan distance (named after the rectangular layout of Manhattan streets) is the distance between two places along a grid. When you travel from home to school, you probably don’t fly in a straight line. Most likely, you follow a street grid, which results in a longer total distance travelled.
Distance can also be measured in relative terms as cost distance. This can include cost in time or cost in difficulty of travel. For instance, cost distance can be calculated by measuring Euclidean or Manhattan distance and then weighting the distance value to account for the difficulty of travel. When walking from your house to the grocery store, you may have two options. Option one may be a flat route of 0.75 miles, while option two may be only 0.5 miles but include a steep hill. Because of the hill, you may add a cost value (either consciously or unconsciously) to give that distance a greater weight. If you decide that walking over the hill is twice as difficult as walking on the flat route, you can multiply the hill route by two (0.5 miles × 2 = 1.0 mile). Based on this calculation of cost distance, you would decide to take the flat 0.75-mile route.
Cost distance can also be measured in terms of time. People often say that they live “twenty minutes” from school rather than saying they live eight miles from school. Geographers use cost distance when calculating drive times. Different types of roads have different speed limits or are made of different materials. A vehicle travelling for twenty minutes will go much farther on a state highway than on a narrow dirt road. For this reason, different road types can be weighted differently for calculating travel time. Also, traffic conditions can vary by time of day, resulting in a cost distance that varies not only over space but also over time.
Figure 1.22.Measuring absolute distance. Euclidean distance in green (1.48 miles) follows a