An aerial photograph is an uninterpreted photo of the terrain. Map production starts with aerial photography, on the basis of which the terrain and the changes therein are interpreted. Aerial photos of various kinds are suitable for different interpretations. Black-and-white aerial photos are most suitable for showing changes in a built environment, whereas colour and infrared photos allow us to interpret the quality of the tree stand and the terrain.
Each year the NLS photographs wide areas from the air, mainly for updating the Topographic database. In 2010, the NLS started a joint purchase of aerial photographs together with the Agency for Rural Affairs (ARA). Thanks to this venture the annual aerial photography increases to 80 000-100 000 square kilometres. Index maps (in Finnish) show the areas to be photographed each year.
Since 2009 a digital aerial camera is used in aerial photography. During one flight the camera simultaneously takes photographs in black-and-white, colour and infrared. These flights are carried out at an altitude of 5 000 m and the topographic resolution of the photographs is 50 cm.
In previous years film cameras were used in aerial photography and most of the photographs were black-and-white. All aerial photographs taken since 1993 have been scanned into digital mode. The NLS archives comprise almost 700 000 aerial photos, the oldest ones dating from 1930’s.
This aerial photography was made 4.5. and 9.5. year 1943. Flights are carried out at an altitude of 2 000 m. Photographs have been digitized and calculated into orthophotos with a terrain resolution of 20 cm.
Accurate aerial photos, or which are known as orthophotos and geometrically correspond to a map, are calculated from aerial photographs. Orthophotos can be reliably used for measuring, for instance, distances and surfaces.
Orthophotos are typically used in mapping and environmental planning and also for monitoring changes. Digital orthophotos are commonly included as an element in geographic information or map production systems.
Orthophotographs are produced according to a sheet line system and their terrain resolution, or pixel size, is generally 50 cm.
Digital aerial photographs have been used to make orthophotos covering nearly all parts of Finland. The orthophoto update index (in Finnish) shows the annual production of orthophotographs.
Since 2009 a digital aerial camera is used in aerial photography. During one flight the camera simultaneously takes photographs in black-and-white, infrared and colour (as in this example picture). These flights are carried out at an altitude of 5 000 m and the topographic resolution of the photographs is 50 cm.
The aerial datasets produced by the National Land Survey (NLS) can be viewed and used on the Internet. Old aerial photographs are found in the archives. Index maps (in Finnish) provide information about photography plans and the coverage of the data.
On MapSite www.karttapaikka.fi users may take a look at the NLS orthophotos free of charge.
Those skilled in the art are allowed to use the orthophotos on Professional’s MapSite and in the browser based Land Information System. External applications can utilize aerial photographs directly through the Service interface of raster layers.
Additional information about the products on: Collections and services (in Finnish).
Inquiries about aerial photos and orthophotos can be made at Information Services of the NLS.