edit: Ok, I won't be so cryptic. Padmapper doesn't copy the posts on Craigslist, they link to them. That's not a semantic quibble. All search engines do so. If I blogged that I was renting my apartment and linked to the Craigslist post describing it, I would be doing exactly what Padmapper is doing.
I think there is a significant difference between copying data, and just giving pointers to CL's data.
However,
If I blogged that I was renting my apartment and linked to the Craigslist post describing it, I would be doing exactly what Padmapper is doing.
This doesn't line up in a few ways. Padmapper is a third-party, not the original poster. There is also a distinction between doing it as a one-off and doing it in an automated fashion.
Padmapper needs to make it trivial for people to "upload" their listings from CL to PM. It could be a single bookmarklet.
Now, suppose that Alice tells Padmapper about Bob's apartment for rent on CL. That's getting even weirder, but PM might be okay if they follow DMCA safe harbour procedures.
Right. I've already agreed that there is a significant difference between displaying copies of CL listings and just having pointers to them.
It doesn't seem, however, that the link is the crux of CL's complaint. Rather it's the fact that PM has copied CL's data in order to generate a mapping of physical locations to CL listings.
You can't copyright data, only its expression. That a certain apartment is available for rent is a fact. The text that appears on the CL website is one expression of that fact. The map that appears on Padmapper is another expression of the same fact.
edit: Ok, I won't be so cryptic. Padmapper doesn't copy the posts on Craigslist, they link to them. That's not a semantic quibble. All search engines do so. If I blogged that I was renting my apartment and linked to the Craigslist post describing it, I would be doing exactly what Padmapper is doing.