Data about the development and state of the Swiss forest were the main products of the National Forest Inventory. It was therefore imperative to care about the quality of data and to spare no effort to collect the best possible data, independent of the type of survey or source. The process of data quality assurance can be roughly divided into three steps: prevention of inaccurate data recording, routine quality control during the data gathering, and data verification before the analysis. All preparation work fell under prevention of inaccurate data recording. For example, the verification and documentation of methods and standards, the planning of the data collection, selection and calibration of working equipment and measuring instruments, evaluation of a suitable computer to collect the data, recruiting of qualified personnel, etc.
During the data collection it was important to ensure that the data were complete, the standards were kept consistent, and that the working equipment and measuring instruments were in good working order. The control surveys, the instruction and training of the survey teams, and periodically visiting the survey teams in the field all helped to meet this goal. Before the data were analyzed they had to be checked to see if they were complete and plausible.