The government notifies you of its intent to take possession of your land to use for a government project. This is legal in some situations, using eminent domain laws.
To do it, the government uses a legal procedure known as "condemnation." It has the ability to use this process because of the power of eminent domain. It's important to understand that the two are similar and they are related, but they are not the same.
One key element to your case, though, is that the government cannot take your land for free. They have to give you "just compensation" for that land.
This is where things can get contentious. What if you bought the property as an investment, and you think you can sell it for $400,000? When government officials contact you, though, they claim that it's worth no more than $250,000. Are you going to have to accept what you feel is a low-ball offer and essentially lose $150,000? Who gets to decide what the property is actually worth?
The only way to get to the bottom of this is to have a valuation done. The goal is to determine what the fair market value looks like at the moment. If you sold it right now, what would you get? That's how much they have to pay.
Naturally, this is a contentious topic. You may still disagree even after the valuation. You may argue that you bought it as an investment in the future. You really didn't want to sell for a few years, when you predict the price will be higher. You still feel like you're losing money, even if the fair market value is accurate.
As you sort your way through all of this, it's critical to know what legal options you have. An experienced attorney can provide valuable guidance.