Open Data License/Legal Structure
The pages compares the proposed ODbL license against the current CC-BY-SA (Creative Commons Attribution-ShareAlike 2.0) licence. CC-BY-SA and the ODbL licence share the same basic tenets - open, share-alike (aka copyleft/viral), and attribution.
This page simply focuses on the details of where they differ and is very much a summary document. You are encouraged to read the licences themselves. Related wiki pages give details of Use Cases, a Time Line to implement the new licence and a FAQ giving the reasons for he change.
Unlike CC-BY-SA, ODbL is expressly enforced through copyright, database right, and contract (2.1). This gives protection in those countries where copyright does not apply to data and databases.
CC-BY-SA does not draw a distinction between the database and the data. ODbL recognise that the two are often treated differently from a legal standpoint, and so provide a companion licence (ODC-Factual) for the data itself. The two would be used jointly in OSM's case.
Why OSMF believes this change is necessary: It is vital that our licence has legal force, in case a company with clever lawyers finds a way to use our data without respecting the intent of the community. Several legal interpretations hold that a copyright-based licence such as CC-BY-SA does not apply to geodata. ODbL provides much more protection here.
ODbL expressly requires that credit is only given to the database, i.e. OpenStreetMap (4.2/4.3). CC-BY-SA, as applied to OSM, is unclear as to whether attribution to every individual contributor is required.
ODbL does offer the possibility of adding other attribution where another substantial data source has been imported (typically not under ODL-Factual). For example, the Canadian Geobase licence requires attribution.
Why OSMF believes this change is necessary: There has been much confusion about attribution requirements and we believe it is possible that, under CC-BY-SA, individual contributors could insist on attribution. At present, we are not complying with this. The ODbL resolves this while still offering a method to incorporate large attribution-required datasets.
When someone takes OSM data and adds their own data to it (forming a "derivative database"), this data has to be made available on the same terms (4.4, 4.4c) - even if their intention was to publish a map and not distribute the data.
This means, for example, that a commercial cartographer wanting to augment their own maps with OSM data would have to publish their own data openly, too.
CC-BY-SA requires that the finished product is made share-alike, but not the source data. Under CC-BY-SA, even if the commercial map was freely copyable, OSM would not get the source data to add to our own database.
Why OSMF believes this change is necessary: We expect use of OSM data to expand rapidly in the years to come. We want to encourage such use and, at the same time, to benefit from it by increasing our data.
If you create a mashup, a video, or a map using OSM data, the ODbL calls this a "produced work" (4.3). In this case, you do not have to share the other parts of the experience (such as the other layers on the mashup, or the artistic cartography). However, you still have to share the map data, as above.
CC-BY-SA requires that the entire "derivative work" is shared. In the past, interpretations of this requirement have stopped OSM data being used as a layer in a commercial mapping website and as part of a TV news programme.
OSMF is asking the licence authors to change the ambiguous wording "more than one source" to "one or more sources".
Why OSMF believes this change is necessary: We wish to resolve one of the most debated aspects of the existing licence, and to encourage use of OSM data in ways that do not damage the project. We believe the approach taken by ODbL is a sensible one.
Note: Parallel distribution
ODbL requires a database protected by "technological measures" - for example, map data in a sealed GPS car navigation unit - to also be made available in unrestricted form (4.6).
Creative Commons believes that OpenStreetMap should use their Open Access Data Protocol licence, which is "a public domain licence with a moral comment". Information on why this approach is not recommended can be found on the FAQ.