x_{1} is the spacial interval/geodesic segment (or line segment/ray/line) from location/point x_{2} to location/point x_{3} in geometry/frame of reference x_{4}.

Like "temci", but for space. "nicfa" yields a vector which encodes similar information (when projected into space). x_{4} can be used, for example, in order to determine whether x_{1} lies across the Earth's surface or cuts through the Earth (like a tunnel) for two distinct city centers. Like "temci", it is essentially just "sirji", but specifically designed in order to pertain to a given measurement-dimension (namely, in this case, space).