Ownership is a matter of public record, and in this case it appears that you erred in reading the town’s maps. The plat maps only show how land is divided; it doesn’t (generally) show who the owner is. And if land is privately owned, the owner gets to dictate who is allowed on it.
In the Portsmouth plat map for Hog Island, plat 172 (which covers the whole island that isn’t covered by one of the lots) has noted next to it “Hog Island, Inc”. So in other words, a private owner. Now, if you cruise over to Portsmouth’s tax assessor database, you’ll find that plat here, which lists the owner, to no surprise, as “Hog Island, Inc.” You can confirm that this is the matching plat because (a) it has the same plat number and (b) one of the buildings on that listing is the island’s boat house:
How do I know this is the island’s boat house? Two years ago it was in the local news when it burned down, and it’s rather iconic on the shore.
Anyways, I’m getting a little off topic here, but it seems the the fundamental error here was in assuming that land not in a little rectangular plot on the plat map was public land. It is not, and demonstrably so, and easy enough to look up.
It is really really important for the good of the project that OSM respects the private access decisions of land owners. Many data consumers, not just mine, use this data. When people turn up on private-access areas because a map said it was a public area, that hurts OSM’s credibility.
It’s not public, it’s not permissive. It’s private, case closed.
I’m citing with permission this conversation I had with a member of the Knight family, who are the long time owners of the majority of the island. I hope this puts this nonsense to bed.
