The US does not have land registration. So, while it's nice that you got a web site with a map, that's worth almost nothing in court.
In contrast the small fee to the Land Registry buys you paperwork that a court of law is compelled to accept as the last word on who owns that land.
In the US if you're absolutely sure you own your plot, but alas somebody else has paperwork which they say proves they own it, you're looking at an expensive court case to find out who is right.
Which is of course why the US doesn't have a land registry, the lawyers and insurers lobby to ensure they get to keep charging people for the peace of mind that they're not going to wake up to find somebody else owns their home.