Data sources: 2016 USA Median Household Income by Esri. Esri, US Census Bureau.
To remember the difference between large- and small-scale maps, either think in terms of ratios or fractions, or use this trick: your neighborhood looks larger on a large-scale map (because it is more zoomed in), while your neighborhood looks smaller on a small-scale map (because it is more zoomed out).
While map scale is important for measuring size and distance and determining the level of detail shown, it is also important to understand scale in terms of how it affects the spatial patterns observed by geographers.
This is often referred to as the modifiable areal unit problem (MAUP). In essence, the unit of measurement used for analysis, be it countries, states, counties, cities, or some other area, can strongly influence the patterns observed on the map. For instance, at a state scale, the “red state/blue state” divide in US presidential elections clearly shows states such as Texas as solidly red (Republican). But by changing the scale of analysis, new spatial patterns emerge. At a county scale, large urban areas within Texas appear as blue (Democratic) patches (figure 1.13). So, while a state level of analysis is useful in understanding the Electoral College for presidential elections, a county-scale analysis is more useful for understanding House of Representative and local election results.
There is no single “proper” scale of analysis for all geographic questions. Rather, the proper scale depends on the question being asked. If the US government has funds available to help states tackle high unemployment, then analyzing unemployment rates at a state level makes sense. On the other hand, if a city government wants to identify neighborhoods with high unemployment rates, then the proper scale of analysis would be urban neighborhoods.
Figure 1.13.Scale of analysis and the modifiable areal unit problem. Explore these maps at https://arcg.is/yDHKy. Maps by author. Data sources: State level—Federal Election Commission. Texas counties—Texas Office of the Secretary of State.
Geographers are interested in spatial patterns at a wide range of scales, always keeping in mind how patterns and processes interact between global and local levels. These interactions have become even more essential to understand due to globalization, the process whereby places become increasingly interconnected through communication networks, transportation technology, and political policies.
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
