Models in AP Human Geography: Purpose and Limitations
Why Geographers Use Models
In the context of the AP exam, a model serves as a theoretical representation of reality. Geographers utilize these tools to isolate specific variables—such as distance, cost, or population density—to see how they influence spatial patterns. For instance, when analyzing urban development, a model helps explain why specific businesses cluster in a city center while residential areas move to the periphery. By using these frameworks, students can move beyond descriptive geography and enter the realm of analytical geography. A key scoring requirement in many FRQs is the ability to apply a general rule to a specific location; models provide the "rule" that allows for this deduction. They function as a laboratory where geographers can test hypotheses about human behavior without the noise of every real-world variable interfering with the results.
Understanding Model Assumptions and Simplifications
Every geographic model is built upon a set of assumptions that create a controlled environment. A common assumption is the isotropic plain, which posits that the Earth’s surface is completely flat, featureless, and possesses uniform soil fertility and climate. This removes the influence of mountains, rivers, or varying resource distributions, allowing the geographer to focus purely on factors like transportation costs or distance-decay. Another frequent assumption is that human actors are "rational," meaning they will always seek to minimize costs and maximize profits. On the AP exam, identifying these assumptions is critical for evaluating a model's validity. If a question asks why a model does not fit a specific real-world scenario, the answer often lies in the violation of one of these fundamental simplifications, such as the presence of a mountain range or a government trade barrier.
Critiquing Models: Eurocentrism and Linearity
Advanced students must recognize that many foundational geographic models were developed in the 19th and early 20th centuries by Western scholars. This often results in Eurocentrism, where the historical development of Europe and North America is treated as the universal standard for the rest of the world. Furthermore, many models assume linearity, the idea that all societies will follow the same path of progress in a specific order. Critiquing these models involves understanding that post-colonial states may face structural barriers—such as debt or lack of infrastructure—that prevent them from following the "typical" stages of development. In an FRQ, demonstrating an awareness of these biases can elevate a response from a basic description to a high-level critical analysis, showing the reader that you understand the limitations of applying Western-centric theories to the Global South.
Population and Migration Models
The Demographic Transition Model (Stages 1-5)
The Demographic Transition Model AP Human Geo (DTM) tracks changes in birth rates, death rates, and total population growth as a country industrializes. Stage 1 is characterized by high birth and death rates, resulting in low natural increase. Stage 2 marks the beginning of the transition, where improvements in sanitation and food supply lead to a plummeting death rate while birth rates remain high, causing a population explosion. This is often triggered by the Industrial Revolution or the Medical Revolution. Stage 3 sees a decline in birth rates as societies urbanize and women gain more education. Stage 4 represents stability with low birth and death rates. Some geographers now include Stage 5, where birth rates fall below death rates, leading to a declining population and an aging dependency ratio. Understanding the DTM is essential for interpreting population pyramids, as each stage corresponds to a distinct shape (e.g., the wide base of Stage 2 versus the "column" shape of Stage 4).
Malthusian Theory vs. Boserup's Hypothesis
Malthusian theory argues that while food production grows arithmetically (1, 2, 3, 4), human population grows geometrically (1, 2, 4, 8). Thomas Malthus predicted that this would inevitably lead to a "Malthusian catastrophe" where the population exceeds the carrying capacity of the land, resulting in famine, war, or disease. In contrast, Esther Boserup offered a more optimistic view, suggesting that population growth acts as a stimulus for innovation. Her hypothesis posits that as population increases, humans will develop new technologies—such as irrigation, fertilizers, or GMOs—to increase food production. This debate is central to modern discussions on sustainability and resource management. On the AP exam, you may be asked to evaluate these theories in the context of the Green Revolution, which significantly boosted agricultural yields and challenged Malthus’s original predictions.
Ravenstein's Laws of Migration
E.G. Ravenstein formulated several "laws" that describe the patterns of human movement. Key among these is the idea that most migrants travel only a short distance, a concept known as distance decay. When migrants do move long distances, they tend to head toward large economic hubs or major cities. Ravenstein also identified the phenomenon of step migration, where a person moves from a farm to a village, then to a town, and finally to a city. Additionally, he noted that every migration flow generates a counter-flow, and that urban residents are less migratory than rural ones. In the AP curriculum, these laws are often linked to the Gravity Model, which predicts that the interaction between two places is determined by the size of their populations and the distance between them. High-scoring responses often use these laws to explain why specific migration corridors, such as the one between Mexico and the United States, persist over time.
Zelinsky's Mobility Transition Model
Wilbur Zelinsky linked the patterns of migration to the stages of the Demographic Transition Model. According to the Mobility Transition Model, societies in Stage 1 of the DTM experience high daily or seasonal mobility but little permanent migration. In Stage 2, as the population surges, there is significant rural-to-urban migration and international emigration to more developed countries. As a country moves into Stages 3 and 4, the primary form of movement shifts to intraregional migration (suburbanization) and interregional migration between cities. This model is vital for understanding the "why" behind global migration trends. It explains that people in developing nations are often pushed out by a lack of opportunity and pulled toward developed nations by the promise of higher wages—a dynamic that shifts as the home country’s economy matures and its population growth stabilizes.
Agricultural and Land Use Models
Von Thünen's Isolated State and Concentric Rings
The Von Thünen model APHG focuses on the spatial distribution of agricultural activities based on economic rent and transportation costs. Assuming an isolated state with a single market, the model predicts that land use will be organized in concentric rings. The innermost ring is dedicated to market gardening and dairy because these products are perishable and expensive to transport. The second ring consists of forest for fuel and building materials, which are heavy and costly to move. The third ring is for extensive field crops like grains, and the outermost ring is for ranching, as livestock can walk themselves to market. The determining factor in this model is the locational rent, or the profit a farmer makes after subtracting transportation costs. As distance from the market increases, the cost of transport rises, and the value of the land for intensive use decreases.
The Bid-Rent Curve Explained
The Bid-Rent curve is the economic foundation of land-use models, illustrating how much a user is willing to pay for land at varying distances from the Central Business District (CBD). Commercial users (retail and offices) have the steepest curve because they require high accessibility to customers and can generate high revenue per square foot. Industrial users have a slightly less steep curve, needing access to transportation hubs but requiring more space. Residential users have the flattest curve, as they are willing to trade a longer commute for cheaper, larger plots of land. This competition for space creates the distinct zones seen in urban and agricultural models. On the exam, the Bid-Rent curve is often used to explain verticality in city centers; because land prices are so high near the CBD, developers build upward (skyscrapers) to maximize the utility of every square inch of expensive real estate.
Modern Applications and Critiques of Von Thünen
While Von Thünen’s logic remains sound, modern technology has altered its application. The development of refrigerated trucking and global supply chains has significantly reduced the impact of perishability, allowing dairy and produce to be grown thousands of miles from their market. Furthermore, the modern landscape is rarely an isotropic plain; highways and rail lines create corridors of accessibility that distort the perfect concentric rings into more of a star shape. Despite these changes, the model still accurately explains why intensive farming occurs on expensive land near urban fringes (where it is threatened by urban sprawl) while extensive farming dominates the rural interior. In an FRQ, you should be prepared to discuss how government subsidies or international trade agreements (like NAFTA) further complicate the simple cost-distance relationship Von Thünen originally proposed.
Economic Development and Industrial Models
Rostow's Stages of Economic Growth
Rostow's model AP Human Geography, also known as the Modernization Model, proposes that all countries follow a five-stage path toward development. It begins with the Traditional Society, dominated by subsistence agriculture. The second stage, Preconditions for Take-Off, occurs when an elite group initiates economic changes, such as investing in infrastructure. The third stage, Take-Off, is characterized by rapid growth in a few limited industries, such as textiles. The Drive to Maturity follows, as technology diffuses to all sectors of the economy. Finally, the Age of High Mass Consumption is reached when the economy shifts from heavy industry to consumer goods and services. Rostow’s model is heavily criticized for being a "top-down" approach that assumes all countries have the same access to resources and ignores the legacy of colonialism that may hinder a country's progress.
Core-Periphery Model and World Systems Theory
Immanuel Wallerstein’s Core-Periphery model (World Systems Theory) offers a structuralist alternative to Rostow. Instead of seeing development as a linear path for individual nations, Wallerstein views the global economy as a single interconnected system. The Core consists of developed countries that control global finance and consume the bulk of the world's resources. The Periphery includes developing nations that provide cheap labor and raw materials to the core. Between them lies the Semi-Periphery, countries like Brazil or India that have some industrial capacity but are still exploited by the core. This model emphasizes dependency theory, suggesting that the wealth of the core is directly dependent on the underdevelopment of the periphery. For the AP exam, understanding this relationship is key to explaining why some countries remain stuck in a cycle of poverty despite participating in global trade.
Alfred Weber's Least Cost Theory of Industrial Location
Alfred Weber’s model focuses on where a factory should be located to minimize costs and maximize profits. He identified three main factors: transportation, labor, and agglomeration. Transportation is the most critical; a bulk-reducing industry (where the final product weighs less than the raw materials, like copper smelting) will locate near the resource to save on shipping costs. Conversely, a bulk-gaining industry (where the final product weighs more, like soft drink bottling) will locate near the market. Weber also considered agglomeration, the clustering of similar businesses to share infrastructure and labor pools. However, if a location becomes too crowded, "deglomeration" may occur as businesses move away to avoid high rents and traffic congestion. This theory is essential for analyzing the shift of manufacturing from the Rust Belt to the Sun Belt or to overseas locations where labor costs are lower.
Urban and Settlement Models
Central Place Theory (Christaller)
Walter Christaller’s Central Place Theory explains the distribution of services based on their threshold (the minimum number of people needed to support a service) and range (the maximum distance people are willing to travel for a service). Low-order goods, like bread or gas, have small thresholds and ranges, leading to many small settlements located close together. High-order goods, like luxury cars or specialized hospitals, have large thresholds and ranges, resulting in fewer, larger cities spaced far apart. The model uses a hexagonal pattern of market areas to avoid overlapping or unserved gaps. On the exam, this theory helps explain the urban hierarchy, where a few large cities provide specialized services to a vast hinterland, while many small towns provide basic necessities to local populations.
Concentric Zone, Sector, and Multiple Nuclei Models
Three classic models describe the internal structure of North American cities. The Concentric Zone Model (Burgess) suggests a city grows outward from the CBD in a series of rings: transition zone, working-class homes, better residences, and the commuter zone. The Sector Model (Hoyt) argues that cities develop in wedges or sectors, often following transportation corridors like rail lines or highways. The Multiple Nuclei Model (Harris and Ullman) posits that a city does not have one single center but multiple nodes of activity—such as a university, airport, or industrial park—that attract different types of land use. These models reflect the evolution of transportation, moving from the walking/horse-car era of the concentric rings to the streetcar era of sectors, and finally the automobile era of multiple nuclei.
Galactic City/Edge City Model
The Galactic City model, also known as the Peripheral Model, represents the post-industrial North American city. As highways were built and car ownership became universal, functions that were once centralized in the CBD migrated to the suburbs. This led to the rise of edge cities—nodes of consumer and business services located along beltways or highway intersections. These edge cities often contain more office space than traditional downtowns. The Galactic City model is characterized by a decentralized urban area where the original CBD is just one of many specialized centers. In an AP Human Geography context, this model is the primary tool for discussing suburbanization, the decline of the inner city, and the emergence of "technoburbs" or high-tech industrial corridors.
Latin American and Southeast Asian City Models
To account for different colonial histories and economic structures, geographers use specialized regional models. The Latin American City Model (Griffin-Ford) features a prominent "spine" of high-end commercial development extending from the CBD, surrounded by elite residential housing. In contrast, the outermost ring is the periférico, characterized by squatter settlements or favelas. The Southeast Asian City Model (McGee) centers on a port zone rather than a traditional CBD, reflecting the region’s history as a hub for maritime trade. It includes sectors for Western businesses, alien Chinese merchants, and mixed-land-use zones. Understanding these models is vital for FRQs that ask you to compare urban morphology across different cultural realms, highlighting how different economic priorities shape the physical layout of a city.
Applying Models to Exam Questions
Identifying the Correct Model for a Scenario
Success on the AP exam requires the ability to quickly match a prompt's scenario with the appropriate geographic model. If a question focuses on the weight of raw materials versus finished goods, you should immediately think of Weber’s Least Cost Theory. If it discusses the lack of development in a former colony, the Core-Periphery model or Rostow’s stages are likely the intended frameworks. Pay close attention to keywords in the stimulus; terms like "perishability" point to Von Thünen, while "infrastructure investment" suggests Stage 2 of Rostow. Identifying the model is the first step in the claim-evidence-reasoning chain required for high-scoring FRQ responses. It provides the theoretical "claim" that you will then support with specific geographic evidence.
Analyzing a Model's Strengths and Weaknesses in an FRQ
Many FRQ prompts will ask you to "evaluate" or "critique" a model. This requires more than just knowing what the model says; you must know where it fails. For example, when discussing the DTM, a strength is its ability to predict general population trends based on industrialization. A weakness, however, is its failure to account for government interventions like China’s former One-Child Policy or the impact of the HIV/AIDS epidemic in Sub-Saharan Africa. When critiquing Von Thünen, you might point to the impact of modern transportation technology. Being able to articulate these nuances demonstrates a high level of spatial thinking and shows the AP readers that you can apply complex theories to a messy, non-isotropic real world.
Connecting Models to Real-World Case Studies
To secure the highest scores, you must be able to ground these abstract models in real-world examples. When discussing the Sector Model, you might point to the historical development of Chicago or the "High-Rent Sector" in many European cities. When explaining the Core-Periphery model, you can use the relationship between the United States (Core) and assembly plants in Mexico (Periphery) as a concrete example. Linking the Central Place Theory to the distribution of Walmart stores versus high-end boutiques in your own region can also make the concept more tangible. These connections prove that you haven't just memorized definitions, but that you understand the fundamental geographic forces that shape the world around you. This synthesis of theory and reality is the hallmark of an advanced student in AP Human Geography.