Hi,

If the council takes a decisioin of expropriating your land, you are offered current market value of the land that is similar other lands around your real estate. But if you think that the offered pay is so lower, you can fill a suit about incresing the pay at civil court of first instance.
The most importantly, and the most debated subject is article 18 of Zoning Law (İmar Kanunu). And unfortunately this artisle is still in force. According to that " If the municipality consider it necessary, it can use private's land until up to %40 of each land to construct roads, parks and etc.
But of course there are some other conditions to apply that article. I advise you to consult an zone-expert lawyer if you face that kind pf problem. Because of the difficulty and complexity of that matter, you will need a knowledgeable attorney.

Best Regards,
Av. Oktay