I try to model a city. I have a group of buildings that act as the hairs of a particle system. The hairs should grow on the faces of a plane. Now this works for the buildings that were initially added to a Group. But later I added two more buildings to this group and these buildings are not "neatly" positioned on the faces of the plane. Either on two faces instead of one face and also on another plane. So it seems that there is something wrong with those buildings
The origin point of these buildings are not at the center of the building's base.
- Place the 3D cursor at this base, for instance snapping it to the selected base
- Then in object mode, choose 'object/transform/origin to 3D cursor'
To say it another way, objects as particle instances are moved/placed so that their origins are following the particle.