Title: Distance
Content: A starting point: library flag pole ; An ending point: statue flag pole ; A direction: -38° ; A distance: 8.72 km Directed distances can be determined along straight lines and along curved lines. Directed distances along straight lines are vectors that give the distance and direction between a starting point and an ending point. A directed distance of a point C from point A in the direction of B on a line AB in a Euclidean vector space is the distance from A to C if C falls on the ray AB, but is the negative of that distance if C falls on the ray BA (i.e., if C is not on the same side of A as B is). For example, the directed distance from the New York City Main Library flag pole to the Statue of Liberty 
Title: Distance
Content:  pole has: Another kind of directed distance is that between two different particles or point masses at a given time. For instance, the distance from the center of gravity of the Earth A and the center of gravity of the Moon B (which does not strictly imply motion from A to B) falls into this category. A directed distance along a curved line is not a vector and is represented by a segment of that curved line defined by endpoints A and B, with some specific information indicating the sense (or direction) of an ideal or real motion from one endpoint of the segment to the other (see figure). For instance, just labelling the two endpoints as A and B can indicate the sense, if the ordered sequence (A, B) is assumed, which implies that A is the starting point.
Title: Geometric terms of location
Content:  path. The shape of the path is not necessarily straight (compare to linear). For instance, a length of rope might be measured in lineal meters or feet. See arc length. ; Longitudinal – spanning the length of a body. ; Orthogonal – at a right angle (at the point of intersection). ; Parallel – in the same direction. ; Perpendicular – at right angles to, synonym to orthogonal. ; Radial – along a direction pointing along a radius from the center of an object, or perpendicular to a curved path. ; Tangential – intersecting a curve at a point and parallel to the curve at that point. ; Transverse – intersecting at any angle, i.e. not parallel. ; Vertical – spanning the height of a body. Common geometric terms of location are:
Title: Distance
Content: Distance traveled: The length of a specific path traveled between two points, such as the distance walked while navigating a maze ; Straight-line (Euclidean) distance: The length of the shortest possible path through space, between two points, that could be taken if there were no obstacles (usually formalized as Euclidean distance) ; Geodesic distance: The length of the shortest path between two points while remaining on some surface, such as the great-circle distance along the curve of the Earth ; The length of a specific path that returns to the starting point, such as a ball thrown straight up, or the Earth when it completes one orbit. "Manhattan distance" is a rectilinear distance, named after the number of blocks (in the north, south, east or west directions) a taxicab must travel on, in order to reach its destination on the grid of streets in parts of 
Title: Expansion of the universe
Content:  obvious that distance is measured by a straight line, but in many cases it is not. For example, long haul aircraft travel along a curve known as a "great circle" and not a straight line, because that is a better metric for air travel. (A straight line would go through the earth). Another example is planning a car journey, where one might want the shortest journey in terms of travel time - in that case a straight line is a poor choice of metric because the shortest distance by road is not normally a straight line, and even the path nearest to a straight line will not necessarily be 
Title: Line (geometry)
Content:   In geometry, the notion of line or straight line was introduced by ancient mathematicians to represent straight objects (i.e., having no curvature) with negligible width and depth. Lines are an idealization of such objects, which are often described in terms of two points (e.g., ). Until the 17th century, lines were defined as the "[...] first species of quantity, which has only one dimension, namely length, without any width nor depth, and is nothing else than the flow or run of the point which [...] will leave from its imaginary moving some vestige in length, exempt of any width. [...] The straight line is that which is equally extended between its points." Euclid described a line as "breadthless length" which 
Title: Distance
Content:  Both distance and displacement measure the movement of an object. Distance cannot be negative, and never decreases. Distance is a scalar quantity, or a magnitude, whereas displacement is a vector quantity with both magnitude and direction. It can be negative, zero, or positive. Directed distance does not measure movement; it measures the separation of two points, and can be a positive, zero, or negative vector. The distance covered by a vehicle (for example as recorded by an odometer), person, animal, or object along a curved path from a point A to a point B should be distinguished from the straight-line distance from A to B. For example, whatever the distance covered during a round trip from A to B and back to A, the displacement is zero as start and end points coincide. In general the straight-line distance does not equal distance travelled, except for journeys in a straight line.
Title: Line (geometry)
Content:  The "shortness" and "straightness" of a line, interpreted as the property that the distance along the line between any two of its points is minimized (see triangle inequality), can be generalized and leads to the concept of geodesics in metric spaces.
Title: Great-circle distance
Content:   The great-circle distance, orthodromic distance, or spherical distance is the distance along a great circle. It is the shortest distance between two points on the surface of a sphere, measured along the surface of the sphere (as opposed to a straight line through the sphere's interior). The distance between two points in Euclidean space is the length of a straight line between them, but on the sphere there are no straight lines. In spaces with curvature, straight lines are replaced by geodesics. Geodesics on the sphere are circles on the sphere whose centers coincide with the center of the sphere, and are called 'great circles'. The determination of the great-circle distance is part of the more general problem of great-circle navigation, which also computes the azimuths at the end points and intermediate way-points. 
Title: Line segment
Content:  When a line segment is given an orientation (direction) it is called a directed line segment. It suggests a translation or displacement (perhaps caused by a force). The magnitude and direction are indicative of a potential change. Extending a directed line segment semi-infinitely produces a ray and infinitely in both directions produces a directed line. This suggestion has been absorbed into mathematical physics through the concept of a Euclidean vector. The collection of all directed line segments is usually reduced by making "equivalent" any pair having the same length and orientation. This application of an equivalence relation dates from Giusto Bellavitis's introduction of the concept of equipollence of directed line segments in 1835.

Question: the length and direction of a straight line between two locations or positions?
Answer: displacement.