When geographers look at a map of houses, stores or farms, they describe the arrangement with three words that are easy to confuse: density, concentration and pattern. This lesson builds on scales of analysis: each of these depends on the area you choose.
Key idea
Density is how many things there are per unit of area (houses per square mile). Concentration is how close together they are: clustered (bunched) or dispersed (spread out). Pattern is the geometric arrangement: clustered, dispersed, random, or linear (along a line such as a road or river).
Why it works
Density is a single number: a count divided by an area. It says nothing about where inside the area the things are. Two squares with 24 houses in 4 square miles both have 6 houses per square mile, even if one has all its houses in two tight clusters. Concentration and pattern describe that arrangement, which density cannot.
Worked examples
Worked example: Computing density
A township of 36 square miles has 540 farms. What is its density of farms?
- Density = number ÷ area.
- 540 ÷ 36 = 15.
- Write the units: farms per square mile.
Answer: 15 farms per square mile.
Worked example: Same density, different concentration
Town A and Town B each have 200 houses on 10 square miles. In A the houses line a main street; in B they are spread evenly over the land. Compare them.
- Density: 200 ÷ 10 = 20 houses per square mile in both.
- Concentration: A's houses are clustered along one street; B's are dispersed.
- Pattern: A is linear; B is dispersed.
Answer: Same density; A is clustered in a linear pattern, B is dispersed.
Common mistake
Students treat density and concentration as the same thing. They are not: changing where houses sit inside a square changes the concentration but not the density. Check: if you can compute it by dividing a count by an area, it is density; if you are describing how bunched or spread out things are, it is concentration.