For instance, global patterns of manufacturing output and employment show dramatic shifts from developed countries to developing countries, especially China and other Asian states. This shift has had a profound impact on development patterns at a global scale, most obviously with the economic, political, and military rise of China. However, these global processes also play out at a more local scale. The shutdown of automobile factories in Detroit has had a devastating impact on that city (figure 1.14).
Myriad impacts, such as massive population decline, abandonment of entire neighborhoods, increases in crime, and municipal fiscal crises have played out locally, all because of global shifts in manufacturing production. At the same time, local-scale impacts in China have transformed many cities, with greater wealth and opportunity combined with pollution of air, water, and soils.
Thus, when deciding the proper scale for creating a map, it is essential to first have a clear idea as to what processes—from global to local—you want to address.
Map projections
Map projections are necessary to transform a three-dimensional spherical globe to a two-dimensional flat map (figure 1.15). If you envision peeling an orange and making the peel flat, you can see that it is an impossible task without tearing and compressing the peel. The same problem arises when going from a spherical world to a flat map.
Figure 1.14.Abandoned Packard automobile factory in Detroit, Michigan. Geographic processes are linked from the global to the local scales. Global shifts in manufacturing have had devastating impacts on some local areas. Photo by Atomazul. Stock photo ID: 154954085, Shutterstock.
Map projections cannot preserve all spatial elements of a map: area, shape, distance, and direction. Just like when flattening an orange peel, something must give. Maps projections that preserve area are known as equal-area projections. These projections show the correct area, such as the square miles of countries and states, but shape, distance, and direction will be incorrect. Projections that preserve shape are known as conformal projections. With these projections, the shape of features, such as country or state boundaries, are correct, but area, direction, and distance measurements will be off.
The Mollweide projection is a good example of an equal-area projection (figure 1.16). Area is preserved, so for example, the square miles within each country are accurate. However, shape, distance, and direction are distorted.
A popular map projection that illustrates the tradeoff between area and shape is the Mercator projection (figure 1.16). This projection is conformal, so shape is preserved, but area is dramatically distorted toward the poles. For example, Greenland appears to be the same size as the entire continent of Africa, while it is actually about fourteen times smaller. ArcGIS Online uses the Web Mercator projection, which is a slightly modified version of the traditional Mercator projection.
Figure 1.15.Map projection. When transforming a spherical representation of the world to a flat representation, distortions are unavoidable. Distortions can be in area, shape, distance, and direction. Images by Esri.
Figure 1.16.Equal-area and conformal map projections. These examples represent an equal-area projection and a conformal projection. Explore the Mollweide projection at http://arcg.is/2m4Q8so. Explore the Mercator projection at http://arcg.is/2l4zdBT. Maps by EsriedtmCF.
Coordinate systems
Given that the major focus of geography is on where things are located, geographers use various types of coordinate systems that facilitate identification of places on the surface of the earth.
Latitude and longitude is the most well-known geographic coordinate system. It allows all locations on the surface of the earth to be identified by measuring angles north and south of the equator and east and west of the prime meridian (figure 1.17).
Latitude is measured from 0 degrees along the equator to 90 degrees north at the North Pole and 90 degrees south at the South Pole. Longitude is measured from 0 degrees at the prime meridian, a line that connects the North and South Poles, to 180 degrees west and 180 degrees east. The International Date Line, which demarcates the change from one calendar day to the next, is located approximately along the 180-degree meridian.
Figure 1.17.Latitude and longitude. This image illustrates longitude lines running from zero degrees at the Greenwich prime meridian to 180 degrees and latitude lines running from the equator to the North and South Poles. Image by NoPainNoGain. Stock vector ID: 326090990. Shutterstock.
Whereas the equator, which splits the earth into northern and southern hemispheres, is a natural location for starting latitude measurements, there is no natural place to begin longitude measurements. Different prime meridians have been used over time, but 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.