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 ...

Many types of sampling methods exist, including random, stratified, cluster, systematic, and convenience, all of which are suited to specific situations. Sampling helps companies make better ...

For systematic random sampling (METHOD=SYS), PROC SURVEYSELECT uses the inverse of the stratum sampling rate as the interval for the stratum. See the section "Systematic Random Sampling" for details ...

With systematic sampling you can then select the points to monitor but this can introduce bias. Random sampling eliminates bias by generating the points randomly. Now you need sampling tools.

CSDS survey, many citizens feel that the government’s resources should be directed towards pressing domestic concerns.