Systematic sampling is a probability sampling method where samples from a larger population are selected according to a random starting point but with a fixed, periodic interval. This sampling ...

If you specify the option METHOD=PPS_SYS, PROC SURVEYSELECT selects units by systematic random sampling with probability proportional to size. Systematic sampling selects units at a fixed interval ...

PROC SURVEYSELECT provides the following methods that select units with probability proportional to size (PPS): PPS sampling without replacement, PPS sampling with replacement, PPS systematic sampling ...

but systematic sampling can be used if there is a trend or pattern across the habitat, such as distance up a beach, or altitude on a hillside. If you are using the wrong kind of sampling method ...