Seattle residents like you may end up in a situation where you wish to possess the land that you're occupying, even if you aren't the actual owner of the land. This is where adverse possession can come into play.
The Legal Information Institute defines adverse possession as a legal process that allows you, the possessor of land, to legally become the title holder even if it's in someone else's possession. Certain requirements must be met as far as common law goes, however. Additionally, you must have been on the land for a decent amount of time before making a move to own it. This amount of time can differ from place to place, but under common law, it is 7 years. If not under color of title, it can be up to 20 years.
Common law also requires your possession of the property to either be open and notorious, actual, hostile, continuous, or exclusive. Open and notorious simply means your possession can't be a secret. Actual means that you actually possess the property, and that the owner has a cause of action for trespassing. Hostile means that your possession infringes on the actual owner's rights. If the owner has given their consent or licensed you, you cannot be in adverse possession. Continuous means that you have never given the property to anyone else and then taken it back. Finally, exclusive means that no one else shares the property with you.
If these apply to you, then it's possible that you could have an adverse possession case on your hands. This will allow you to fight for property ownership.