Yahoo! Aerial Imagery
|Yahoo imagery is no longer available
as of 13 September 2011: 
Yahoo! provides Vertical Aerial Photographs as part of their map services, and allowed this to be used within Potlatch and formerly standalone OpenStreetMap editors. We were able to trace from yahoo to more quickly and accurately create maps in some parts of the world, and we are very grateful to Yahoo! for this support during the crucial early years of our project's development between 2007 and 2011.
In September 2011 Yahoo partially shut down their aerial imagery service and/or replaced their imagery with such from a new source. WE DO NOT HAVE PERMISSION TO USE ANY CURRENT YAHOO IMAGERY! Luckily we have, since 2010, had a similar agreement with Bing (Microsoft). On the whole bing's imagery is superior, although not everywhere. Cities in Pakistan for example were covered by the no-longer-available Yahoo imagery, but are not available (at hi res) in bing.
Yahoo! never exactly gave us explicit permission, but stated that their terms and conditions allow using their aerial imagery (blog announcement about it) for the purposes of tracing. We could use any of the three main OSM editors (Potlatch, Merkaartor, or JOSM), to edit OSM map data over the Yahoo! imagery.
The availability of the Yahoo! imagery made possible a number of tasks which would most be almost impossible without it. Some of these achievements are listed here:
The whole of the original London Congestion Charging Zone was mapped over a single weekend by a team of people using Yahoo! imagery. London is notoriously difficult to map using conventional GPS-based methods due to the urban corridor effect giving poor traces.
- Baghdad maps
The whole road and rail network of the Baghdad area has been mapped using the Yahoo! imagery. As have some parks, forested areas, etc. People on the street are showing real interest in filling in the road names to make this an actually useful map, it's not just a promotion piece.
- Mashhad, Iran
The whole road and rail network of the Mashhad, Iran area has been mapped using the Yahoo! imagery. As have some parks, forested areas, etc. Street and place names are slowly coming in as well. A GPS-track was used to verify that the Yahoo! imagery indeed was accurate and has very little (<2m) offset in that area
- St Albans and surrounding area
Not quite so grand as the above cases, but every last bit of woodland, every golf course, every lake and the main rivers/streams/lakes were mapped, which isn't possible with Landsat and would be very laborious by ground-based surveys.
- Sydney and surrounding area
Completion of the greater metropolitan railway network, completion of the inner city unclassified road network, many arterial major roads that were previously in as stretches here and there, several complex road interchanges not practical to map on the bike, several major rivers (also strangely difficult to map on a bike) and adjusted many problems due to inner city urban canyoning. Plus a good few golf courses, parks and sports pitches. At the AU$160/km2 rate quoted for Australian 2m resolution imagery, that would have cost AU$300,000.
- Darwin to Port Augusta (Australia)
Using the new Potlatch editor the highway between Darwin and Port Augusta (ie the whole of the central North - South Highway), together with the highway to Ayers Rock & the Olgas, has been completed. Most of the imagery is low resolution. (The road has now been surveyed along stretches and has been nudged and tagged accordingly.)
The imagery covered the whole of the U.S., but elsewhere it generally covered only rectangular areas around some cities. See the list documenting Yahoo! Aerial Imagery/Coverage.
Yahoo!'s aerial imagery is pretty accurate. More so than consumer GPS units in general. In some parts of the world (e.g. Italy) there is noticable offset though, much more than simple consumer GPS units. For more detail see: Yahoo! Aerial Imagery/Accuracy.
Note that as of late 2011, Yahoo have shut down their mapping unit. The following does not apply to any new yahoo offerings and new editing activity within OSM. The details are kept here for historical interest, and because the nature of these past agreements is pertinent to existing OpenStreetMap data.
Yahoo took the position that if we derive vector-based map data from the aerial photos owned by Yahoo! they are no longer copyright Yahoo!, so we could release our data under any license we want, CC-BY-SA, ODbL, ... Anyone who has traced from Yahoo imagery may accept our new contributor terms and does not have to change their contributions.
Yahoo's last statement on the legalities, from Scott Regan, was..
Mikel originally worked on liaising with Yahoo! people about this agreement. His comment was:
- "Even though there are open questions, I suggest that we can continue as we have confidently. OSM continues on even with the outstanding questions about attribution, etc. The use of Yahoo! imagery can continue as well. The spirit of what we are doing is sound, there are only particulars which need sorting out"
- Also from Mikel: "There's multiple individuals, project managers and lawyers, involved in the decision. The first pass on the subject was a more cautious reading of the ToU, but at request, they (Yahoo) invested significant time in re-examining the particulars."