The requirements for national forest inventories have changed in recent decades, as have the issues involved. Initially, the focus was mainly information on timber resources, but today social and environmental functions are also of interest. An a priori separation of the surveyed areas into forest and non-forest during data collection limits the interpretation of the tree resources. Not all trees are located in the forest and not all forests are fully stocked. In the aerial photo interpretation of the 3rd National Forest Inventory, land cover on a regular sampling grid was determined regardless of the land use. This allowed, for the first time, nationwide information on tree resources to be obtained, independent of forest definitions. The tree cover of Switzerland is 27.0% regardless of whether the trees are in the forest or outside. The area covered with forest (proportionally 29.4%) is larger than that covered with trees. The location of the trees outside the forest tends to be mostly either very close to forest or in urban areas. The most densely stocked areas, after forests, are urban areas. The data from aerial photo interpretations of the 3rd National Forest Inventory allow a more nuanced picture of the stocking over the whole country, but the sampling error is still too large to draw conclusions for small areas. The existing and ongoing surveys, however, provide a calibration and reference dataset so that, with remote sensing data and methods, it should be possible to generate more comprehensive spatial datasets to help to fill this gap.