LINESTRING4

LINESTRING4 is a term used in some geographic information system contexts to denote a linestring that consists of exactly four vertices or coordinate positions. It is not an official geometry type in the core standards (such as ISO or OGC); rather, LINESTRING4 is a convention that appears in certain datasets, tutorials, or software to emphasize a fixed vertex count for a polyline.

In practice, LINESTRING4 represents a standard two-dimensional or three-dimensional linestring with four points. Each point is a coordinate pair (x, y) in 2D, or (x, y, z) in 3D, and may also include an optional measure value M in some systems. A LINESTRING4 therefore contains three line segments, connecting the points in order: from point 1 to point 2, point 2 to point 3, and point 3 to point 4. The number of points can be varied in a generic LINESTRING, but LINESTRING4 fixes it to four for consistency in certain applications.

Representation in common formats follows standard LINESTRING syntax. In Well-Known Text (WKT), a LINESTRING4 might appear as LINESTRING(x1 y1, x2 y2, x3 y3, x4 y4), and in GeoJSON as a LineString with four coordinate tuples: [[x1, y1], [x2, y2], [x3, y3], [x4, y4]] (and with z if 3D). Calculations such as length, distance, or angle use the same methods as for any LINESTRING, summing the distances between successive points.

LINESTRING4 is primarily a naming convenience rather than a separate data type; any four-point polyline can be represented as a standard LINESTRING in most GIS tools.