My gosh, it's ridiculous how many people on this site think they're suddenly lawyers any time something about intellectual property comes up (note: I'm not talking to those of you who have rightly said that this guy does have a copyright claim).
Just because you've read some articles that mention intellectual property doesn't mean you know the law. The law does not always follow your personal logic, conscience, ethics, beliefs, etc. It's incredibly unproductive when people with no legal education comment as if they are giving a factual account of the law. It's silly, lazy, and, worst of all, it perpetuates that misinformation.
This guy probably has a damn good case (I can't say anything for sure since I, like the rest of you, can't possibly know every fact in the case). First off, those of you saying he merely changed a couple of things on the map should actually compare the original and his map before actually making that assertion. The changes he made were quite significant, not only from an aesthetic point of view, but from a legal one. The changes are sufficient to make it an original work under the law.
For those saying that Naughty Dog might have just made an honest mistake, this is an understandable view, but it's almost completely certain not to be the case. Videogame companies are very well-versed in intellectual property law. A company like Naughty Dog likely has in-house lawyers to work on this stuff (and, even if they don't, it doesn't really matter). They know what can and can't be used without permission, and they know better than to simply do a search on something and then assume they can use it because it turned up on google (heck, even most of the people here know that).
For those saying that this is just a case of some guy trying to "extort" money from someone who is more successful: what's your point? First off, it's not extortion. Let's just get that straight. This guy created an original work, and somebody else used it without permission or payment. That is illegal, no matter who you are. To design the map themselves would have taken labor and time, which costs what? It costs MONEY. They avoided paying that money by using his work; therefore, the money should go to him, as he did work for them that otherwise would have to be done by actual paid employees. Just because ND has a successful game out does not in any way mean that they get to do what they want when it comes to the law. Could you imagine what kind of world this would be if your philosophy was actually the prevailing wisdom?
Finally, for those who say it's just a small part of the game: again, what's your point? So, if someone steals your work, but uses it as just a small part of a larger work, that's ok? Just because it's a small part of something larger means that they shouldn't ask for your permission or pay you for the work you did, which they would otherwise have to pay to someone else to use their work?
As the facts stand before us right now, ND stole from this guy. It's as simple as that. Nothing else matters. Not your personal beliefs, not the work's significance in the whole of the game, not whether the work was based on a different map, not whether you believe certain things about the law that aren't true.
EDIT: and, of course, I would be remiss not to add one more comment about the sad, cruel irony of people defending a videogame company stealing intellectual property from some single graphic designer in MA.
EDIT 2: considering the effects the gaming community has had on both EA's policies (their recent decision to back away from insisting on online passes) and Microsoft's next console, people should really be happy that they have more of a voice than they thought and that they might sometimes actually be able to change the predatory practices of these huge videogame companies. Instead of defending ND with fallacies and faulty legal reasoning, people should stand against game companies appropriating the works of others to fill out their games instead of paying someone to do that work or paying to obtain work that has already been done. Remember, one day you might be trying to live off your own creativity, only to find that someone is stealing your work for their own uses, AND the projects in which they're used end up making a ton of money. You won't feel so good about it then.