There are three axes (dimensions) of motion with six degrees of freedom. There are two metrics of motion: a length metric and a duration metric. The length metric is the magnitude of the vector between two points, and is called distance. The duration metric is the magnitude of the vector between two instants, and is called distime.
If one conceives of this as two 3D metric geometries of motion, then there is a 3D length space geometry with a distance metric and a 3D duration space geometry with a distime metric. If the speed of light is an absolute conversion between distance and distime (which is essentially Einstein’s second postulate of special relativity), then there is one 6D length-duration metric geometry.
A 3D length space coordinate system is built from an origin point and three orthogonal axes with a distance metric. A 3D duration space coordinate system is built from an origin timepoint and three orthogonal axes with a distime metric. A 6D length-duration coordinate system is built from an origin event, three length space coordinates, and three duration space coordinates. Either the three duration coordinates may be converted to lengths, or the three length coordinates may be converted to durations.
A placeline represents two opposite linear motions with a constant rate (i.e., inertial motions). The positive direction represents distances to events diverging away from the origin point. The negative direction represents distances to events converging toward the origin point (i.e., destination). Apart from motion a point has a distance but its sign is ambiguous. A placeline represents the placepoints of an odologe.
A time line represents two opposite straight motions with constant rate (i.e., inertial motions). The positive direction represents distimes to events diverging from the origin instant. The negative direction represents distimes to events converging toward the origin timepoint (i.e., destination). Apart from motion an timepoint has a distime but its sign is ambiguous. A time line represents the time or scalar time of a clock.
Events may be ordered by the stance or the time. Events ordered by placepoint are placelined. Events ordered by time are timelined. All events that are equal distances (equidistant) from the origin point are simulstancious with it. All events that are equal distimes (equidistimed) from the origin timepoint are simultaneous with it.