The Swedish National Forest Inventory is based on a systematic sample. An inventory is undertaken on sample plots and this forms the basis for both area and volume estimates.
The sample plots are circular and are, for practical reasons, grouped into clusters (tracts). The tracts are square or rectangular in shape and are of different dimensions in different parts of the country. The number of sample plots per tract also varies for different parts of the country.
The permanent tracts are revisited every 5th year and are laid out in a systematic grid covering the country (with a random starting point), whereas the temporary tracts, which are only visited once, are randomly distributed but with consideration for the permanent tracts.
The Swedish Forest Soil Inventory is a detailed soil survey which is undertaken on subset of the National Forest Inventory sample plots. The Department of Soil and Environment, SLU is responsible for the scientific content of the National Forest Soil Inventory.