Spatial Distribution in AP Human Geography

Density, concentration, and pattern as three separate descriptions

Each property answers a different question about the same map.

• Density is the frequency of something per unit of area, like people per square kilometer or farms per square kilometer.
• Concentration is how spread out things are relative to each other. Clustered (agglomerated) means close together, and dispersed means spread apart.
• Pattern is the geometric arrangement, such as linear along a river or highway, a grid in a planned city, or random scatter.

The term comes from Unit 1: Thinking Geographically. It sits at Topic 1.4 (Spatial Concepts), where pattern is one of the ideas used to describe how things relate across space. It also connects to Topics 1.2 and 1.3. Topic 1.2 covers collecting geographic data through methods such as fieldwork and geospatial technologies, and Topic 1.3 covers how data such as census figures and satellite imagery inform decisions at different scales. The rest of the course takes the same approach and applies it to new subjects.

Same density, different distribution: the mix-up to avoid

Density is one number. Spatial distribution is the whole arrangement, and density is only one piece of it.

Two neighborhoods can each have 20 houses on the same amount of land, which gives them identical density. If one has the houses packed into a corner and the other has them spaced evenly, their concentration is completely different.

Egypt is the classic population example. Divide its population by its total land area and you get a moderate density figure. That number hides the real distribution, because most Egyptians live in a narrow band along the Nile and in the delta, while most of the country is sparsely populated desert. This is why Topic 2.2 asks you to explain how both distribution and density affect services like medical care and the land's carrying capacity. A question that asks for people per square kilometer is about density. A question that asks how people are arranged on a map is about distribution.

Describing a mapped pattern, then explaining it

Maps and data sets showing distributions are common stimuli. In Section I, a stimulus-based multiple-choice question might show a distribution and ask which concept or process explains it. One practice question gives a tech company's customers: 70% within 50 km of its Silicon Valley headquarters, 20% at 50-200 km, and 10% beyond 200 km. The concept that explains this is distance decay, because interaction drops off as distance from the origin grows.

In Section II, Question 2 (One-stimulus question) and Question 3 (Two-stimuli question) can hand you a map or data set and ask you to describe and then explain what it shows. A strong answer names the pattern precisely, for example "clustered in coastal cities" or "linear along the rail corridor." Then it connects that pattern to a process or model from the relevant unit. If you describe the pattern but give no reason for it, you've answered only half the question.

Watch the scale too. Each free-response question covers at least two units, and at least two of the three require analysis across geographic scales. A distribution that looks dispersed at the national scale can look tightly clustered at the local scale.

The distributions each later unit asks you to explain

Agriculture (Topics 5.1 and 5.7) explains where farming types occur. Physical geography is one reason, since Mediterranean and tropical climates support different crops. Economic forces are another, as large commercial farms replace small family farms.

Cities (Topic 6.4) use the rank-size rule, the primate city, gravity, and Christaller's central place theory to explain how big cities get and how they're spaced. Central place theory predicts that small service centers sit close together and larger centers sit farther apart. Topic 6.6 applies the same thinking inside a city by looking at where low-, medium-, and high-density housing sits.

Governance (Topic 4.7) describes how power is distributed. Unitary states concentrate it at the center, and federal states spread it across more local centers of authority.

Industry (Topic 7.1) explains why early industrialization clustered where natural resources were available, then spread outward with new technology.