Most ecological surveys have some degree of stratification incorporated into the design. A stratified sampling design can work as a framework for either a systematic or random design. This is especially true if the measurements within the strata are homogeneous. Cost per observation is normally reduced. If estimates of population parameters are desired for subgroups of the population, separate estimates can be obtained for each.
Stratification is encouraged when doing species inventory in British Columbia.
These can be derived from existing maps, such as Site Series or Forest Cover polygons, or customized from aerial photos. The goal is to delineate habitat strata which are homogenous with regard to species abundance or distribution. Although this type of stratification may have a relationship to habitat, it may not necessarily be reflected by similarities in habitat between similar strata. Strata are usually labeled as High, Medium, Low, and Nil densities. The basis for stratification is generally most meaningful for territorial mammals with large home ranges which are the focus of long-term monitoring.