The national maps are updated after the topographic landscape model has been updated. For technical and personnel reasons within swisstopo, and in view of the topographic characteristics of the country, Switzerland has been divided into “update blocks”.

The distribution of the individual sheets within each update block is based on the most practical distribution of the Alpine sheets. In the mountains, because of snow cover the period during which flights and surveys can be carried out is much shorter than in the lower-lying areas.

Changes are recorded, supplemented with data from other available sources, verified and integrated into the topographic landscape model, which forms the basis for obtaining data for updating the national maps.