I don’t often wade into the flame war territory of vi vs. emacs, GPL vs. MIT (etc.) and the question of “more open” for a given definition of open. But, as State of the Map, US (SOTMUS) approaches, the question of the share-alike clause with it’s copyleft equivalency in OpenStreetMap seems to rise as a conversation piece. For example:

Share alike is one of those features you only want if you have it

— Alex Barth (@lxbarth) March 13, 2014

and of course this:

#OpenStreetMap isn't all that open. Let's change that and drop share-alike http://t.co/WAOPvAX6oC

— Alex Barth (@lxbarth) March 13, 2014

So, the copyleft. It’s an assertion of copyright, but with a radical twist. It’s a tool in the toolkit, and important. It’s used to good effect in Linux and PostGIS and other important projects. I’m no purist– there are undoubtedly times when copyleft prevents the growth and contribution of community. It’s important because it is a protection of that which we make public to remain public.

The same is true for share-alike. This is like enabling legislation is for governmental agencies, it’s a line in the sand that defines that which is a public good vs. private good.

Assuming it gets accepted as a pull request, you’ll be able to use CC0 or ODbL (share-alike) for data on GitHub in a drop-down soon… .

So, when does share-alike or copyleft make sense? Maybe when the thing needing protection is a core piece of data or software (PostGIS, Linux, etc.). And (from the perspective of a not being a nearly active enough OSM member) perhaps OpenStreetMap fits here too.

Let the argument begin. CC0! Share-alike! CC0! Share-alike!