What is Area Sampling?
Area sampling involves sampling from a map, an aerial photograph, or a similar area frame. It is often the sampling method of choice when a sampling frame isn’t available.
For example, a city map can be divided into equal size blocks, from which random samples can be drawn. Although area sampling is most often associated with maps, sometimes the samples might be drawn from lists (Särndal & Swensson, 2003).
Two common random sampling methods used to sample within areas are stratified random sampling and sampling with a probability proportional to the size of the area.
Clusters and Subsampling
The samples drawn from an area frame are often referred to as clusters. These clusters may be subsampled several more times.
For example, let’s say you wanted to sample from a population of middle school students. The first sample might be drawn from a list of school districts, the second sample from a list of schools, the third a list of classes and then finally a list of students within those classes. The “frame” in this example is the four successive layers.
Advantages and Disadvantages of Area Sampling
Although area sampling using area frames is often the method of last resort, it does have a few distinct advantages:
- Area frames can be used for multiple variables at the same time. For example, an area sample on a city can collect data on land use, population and income statistics.
- There’s no overlap between sampling units; Every unit has an equal chance of being selected. This complete coverage results in unbiased estimates.
- Although the area frames can be used in subsequent surveys, they can quickly become outdated (for example, if a city undergoes tremendous growth).
- Area frames can be costly to build.
- Outliers can be a problem, especially if your map has a few particularly dense or sparse areas (for example a city that has a national park in its boundaries might have zero population in some areas and a huge population in another.
D’Amico, V. (2000). Marketing Research. Tata McGraw-Hill Education.
Davis, C. (2009). Area Frame Design for Agricultural Surveys. Retrieved November 5, 2019 from: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.400.6067&rep=rep1&type=pdf
Särndal, C. & Swensson, J. (2003). Model Assisted Survey Sampling. Springer Science & Business Media.