Selects the area for which the force_element_edge_normal record with the same index should be applied. By example, -geometry_line 1 can be used in 2D, indicating that the nodes on line 1 get the distributed force.
Attention: if this force_element_edge_normal_geometry option is used INSIDE a FE mesh, then the elements on each side of the geometry will get the force. So the total force will normally become zero since the normals of the elements at the side of the geometry are opposite.