# The Difference Between Spatial Distribution & Density

Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Spatial distribution and density are both methods used to describe populations. And while they are related, they are not the same. In this lesson you will learn about both, as well as how they are different from each other.

## Population Distribution

When we study populations - be they groups of humans, animals, plants, or otherwise - there are several important factors to consider. And this includes how these populations are spread out, or dispersed. We can talk about this dispersion in two main ways: spatial distribution and density.

Spatial distribution describes where a population is located. For example, we can talk about the spatial distribution of a population throughout the state of Michigan, along the Great Barrier Reef, or in a tiny remote village that covers 50 square miles. Density, on the other hand, describes how many individuals are in that given space. We might say that there are 100 people per square mile, or 20 plants per square inch. This gives us an idea of how tightly or loosely packed the organisms are in a given space.

Many things will influence both spatial distribution and the density of a population, so let's explore these two concepts in a bit more detail.

## Spatial Distribution

I want you to think for a minute about people on Earth. We inhabit just about every corner of the planet, but this is only possible because of modern technological advances in things like clothing, food storage, and transportation. Nowadays we can visit places like Antarctica and the Sahara Desert because we can get ourselves there efficiently, we can protect ourselves from the extreme climates, and we can traverse large landforms with different types of equipment. But if you didn't have any of these things you would be out of luck, right?

Climate, topography, the ability to move from one place to another, landforms, and other natural barriers are all limiting factors for populations in terms of where they can set up shop. And this is true for all populations, be they plant, animal, whatever. They can only live where they can get to and survive. This is exactly why you don't find polar bears in tropical rainforests or whales in the Rocky Mountains. In other words, limiting factors restrict a population's spatial distribution.

For humans, there are social factors that influence spatial distribution as well. Political boundaries, economics, cultural factors, and even language all play a part in where certain people can or cannot go. Which brings up another important point: populations can be described in many ways! We can talk about the entire human population as a whole, or we can discuss smaller groups of people as populations as well. And each population we describe will have its own spatial distribution based on both human and natural factors.

## Population Density

While it is different from spatial distribution, population density is also related to it. That's because now you're looking at how many individuals are within that space you were describing. So if the spatial distribution covers 2 square km, then the density would be how many individuals are within that 2 square km area. We derive population density by dividing the total number of individuals by the total area they take up. So if there are 100,000 people in our 2 square km, then we would say the density is 50,000 individuals per square kilometer. Population density is an average, which is a good way to describe the population because generally the spread is not uniform across the spatial extent.

Density can be measured for anything as long as you know the number of individuals and the size of the area they take up. We can measure the density of a certain type of tree in the forest, the density of fungi growing on one of those trees, the number of squirrels living in your backyard, etc.

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