map generated is not continuous

 And the one containing the laser scan (red points) is like this:  Im using gmapping and the laser data is got from my Velodyne-16. I first projected it to 2D laser then use it for Gmapping. But in the map, the wall is not continuous. I know that its actually occupancy grid map and is not continuous but this map can be distinguished just by eye. So I thought there must be something wrong, especially this map works pretty bad for later localization. Below is my params setting. Anyone has any idea is very welcome!