1)how far is it true that a piece of land that has not been used for more than 3 years may be taken by one who will develop it? 2) what are the conditions attached to it?
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
If this land belongs to a person, then no one has the right to take it away from him even if it had not been used for hundreds of years. However, if this land does not belong to anyone and it is a “no man's land”, and a person puts his hand over it [possesses it] in order to revive it, and puts stones around it [as a boundary], or plants wood around it, wires or any other method that is considered by the scholars as a method of assigning a “no man's land” to a specific person, then it becomes his, unless he does not revive it for a long duration (according to people’s customs), like three years. In such case, the Muslim ruler should tell him: ''you either revive it and become its owner, or leave it for someone else, if any, who will revive it.”, as was stated by many scholars such as Al-Buhooti .
Finally, it should be noted that this matter is well known and is found in all Islamic jurisprudence books. However we do not think that any Muslim country act upon this any longer; rather, property ownership is decided according to the laws of each country.Allaah Knows best.
You can search for fatwa through many choices