Orthophoto (aerial image)

An orthophoto is an aerial survey photo that has been re-projected to remove distortion caused by perspective and uneven terrain. It can therefore be laid directly onto a map, and distances and areas can be measured on it. The Orthophoto of the Czech Republic is produced within the sector of ČÚZK, the Czech Office for Surveying, Mapping and Cadastre, in cooperation with the ministries of defence and agriculture; the images are processed by the Land Survey Office (Zeměměřický úřad) and the military geographic office in Dobruška.

How the images are made and how old they are

Since 2012 the country has been photographed in a two-year cycle: roughly half of the territory each year, so the current orthophoto is usually one to two years old. Since 2021 one pixel represents 12.5 cm on the ground; in 2016-2020 it was 20 cm and earlier the images were coarser.

Besides the current orthophoto, ČÚZK provides archive orthophotos, according to its technical report going back to 1998. For an even older view there is a historical orthophoto map from the 1950s, assembled from military archive aerial photos and published as a map service by CENIA, the Czech environmental information agency. For the period around 1840 there is the hand-drawn map of the Second Military Survey.

What an orthophoto shows

• how the area has changed: where houses were built, where an orchard disappeared or a forest grew
• what is on the neighbouring plots and what the access road looks like
• the extent of the garden, paved areas and greenery at the time of imaging

What to watch out for

An orthophoto is a picture, not a boundary survey. Plot boundaries belong to the cadastral map, and the two layers can differ slightly, especially where the map has lower boundary accuracy. Trees and shadows may hide part of a plot, and buildings constructed after the flight are missing. The image does not show building heights or terrain slope; that is what the digital terrain and surface model is for. Always check the year the image was taken.

Frequently asked questions

Is an orthophoto the same as a satellite image?

No. The Czech orthophoto is made from aerial survey photos taken from an aircraft, not a satellite, and is geometrically corrected for accurate measurement. Imagery in common map apps may have a different origin, age and accuracy.

Can an old image show whether a building was permitted?

No. The image only shows what stood on the site at the time. Whether a building was permitted and approved for use has to be checked in the records of the building authority.