The land ownership data comes from the state/county Cadastral and is only as accurate as the cadastral. I have seen where a surveyed corner was 50' off from the GPS coordinates. Probably would not result in a trespassing citation as game wardens and such use the same data base, but can make a significant difference in a legal access claim and/or whether a parcel of land can be insured with title insurance in a land transaction without additional proof of survey.
Very true. I bought some land in central Montana a few years ago and relied on the Cadastral rather than a survey. The Cadastral showed the land being on both sides of a trail, with about 200 ft of the land on the west side of the trail and the rest of the land to the east. So based on that, I bought then had a log cabin builder take a look at the land and find a good place to put the cabin as it was being built. It turned out they thought the 200 ft on the west side of the trail was the best location.
When they hauled the cabin out to the land and started to prep the spot for placing the cabin, the guy who owns the adjoining land asked them if someone just bought the land, as he had been misled by the Cadastral when he bought his land and had an actual survey done. That survey showed that the land boundaries were off and my land did not include the 200 ft west of the trail.
That was a close call, as I wouldn't have wanted to have had to move the cabin and clean up the mess I made on the other owner's land.
