Sampling

Sampling is the selection of a subset of the population (sample) that is considered representative of the group to which they belong. It is done so in order to study or determine the characteristics of the entire population. Consequently, sampling also includes deciding on the locations of a certain area where samples should be taken from.

When “sampling” different methodologies can be used to select the locations to collect samples from:

• Random: Samples are taken randomly from the study area.
• Systematic: The locations for sampling are chosen using a certain pattern (grid).
• Stratified: Before choosing the locations, the area is divided in groups according to certain variables/parameter (for example if we are only interested on areas above a certain altitude).
• Subjective: Areas are chosen for non-objective reasons.

Random and systematic sampling methods are useful when the knowledge about the system of study is restricted. However, if interpolation techniques or the creation of a gradient map of an area is needed, a systematic sampling is typically the best option. Importantly, stratified and subjective methods require a high level of initial knowledge of the study area.