There is provided mechanisms for location based mobility measurement activation. A method is performed by a network node. The network node is configured to provide network access in a first cell. The method comprises determining, according to information of at least one measurement area, whether wireless devices are to perform mobility measurements for a possible handover to another network node or not. Each of the at least one measurement area has a dynamically changeable size. The size depends on position dependent events of the wireless devices in the first cell. The method comprises providing mobility measurement activation instructions to the wireless devices in the first cell in response thereto.