Prague Institute of Planning and Development is an organisation representing the city in spatial planning matters. They publish vast amounts of data through the website Geoportal under CC BY-SA 4.0, including regularly-updated high-resolution aerial imagery of the entire city.
Just over a year ago I noticed that there were some attempts to negotiate a permission to use their imagery for OSM, but the last news from that front was almost a year old. Being the sort of a person who tends to ask questions first and ask questions later, I decided to write them an email to find out what state were the negotiations in.
I listened to their reasons for keeping the data under CC BY-SA 4.0 and a few reassuring emails later I received an email containing the following:
"IPR Praha souhlasí s využíváním ortofotografií, které poskytuje prostřednictvím Geoportálu hl. m. Prahy, za účelem aktualizace a doplňování databáze OpenStreetMap, přičemž vzniklá vektorová data smí být vložena do OSM pod licencí ODbL za předpokladu, že IPR bude uveden v seznamu přispěvatelů do OSM a takto vzniklá data budou mít IPR uveden jako svůj zdroj."
A simplified translation for the non-Czech-speakers out there:
"[The Institute] agrees with the use of aerial imagery provided through [the website] for OSM. Resulting vector data may be published by OSM under ODbL provided that [the Institute] will be listed among the contributors to OSM and the data will list the appropriate source."
Needless to say I had the contributors wiki-page edited almost immediately. And so we got ourselves some very shiny imagery to use.
This January I had a look at the list of changesets and found that, in 2017 alone, at least 27 users used the imagery for a total of over 500 changesets and causing over 56 thousand map changes. When I wrote back to the Institute to share these stats with them, the resulting conversation ended with the granting of a general permission to use any of the CC BY-SA 4.0 data from the Geoportal website under the same conditions.
And that is the story of how OSM got its access to a lot of data for Prague.
I'd like to thank Prague Institute of Planning and Development for their generosity. We are grateful for this data and even I am curious as to what we can make with them.