Complex sentence: Since January 1,2011 Oost-Maarland is one of the population centres in the Eijsden-Margraten municipality; before it was in the Eijsden municipality, that on the mentioned date has merged with the neighbouring municipality of Margraten.
Split into simpler sentences: Since January 1,2011 Oost-Maarland is one of the population centres in the Eijsden-Margraten municipality. Until then it was in the Eijsden municipality that merged with the neighbouring municipality of Margraten.