Geometry Well-Formedness and Validity •Polygon rings can be specified both clockwise and counterclockwise. MySQL flips the rings automatically when reading data. Cartesian coordinates are stored in the length unit of the spatial reference system, with X values in the X coordinates and Y values in the Y coordinates. Axis directions are those specified by the spatial reference system. Geographic coordinates are stored in the angle unit of the spatial reference system, with longitudes in the X coordinates and latitudes in the Y coordinates. Axis directions and the meridian are those specified by the spatial reference system. The  LENGTH()  function returns the space in bytes required for value storage. Example: The value length is 25 bytes, made up of these components (as can be seen from the hexadecimal value): For geometry values, MySQL distinguishes between the concepts of syntactically well-formed and geometrically valid. A geometry is syntactically well-formed if it satisfies conditions such as those in this (nonexhaustive) list: A geometry is geometrically valid if it is syntactically well-formed and satisfies conditions such as those in this (nonexhaustive) list: •Linestrings have at least two points •Polygons have at least one ring •Polygon rings are closed (first and last points the same) •Polygon rings have at least 4 points (minimum polygon is a triangle with first and last points the same) •Collections are not empty (except  GeometryCollection ) •Polygons are not self-intersecting • 8 bytes for double-precision Y coordinate ( − 1) •8 bytes for double-precision X coordinate (1) •4 bytes for integer type information (1 =  Point ) •1 byte for integer byte order (1 = little-endian) •4 bytes for integer SRID (0) mysql>  SET @g = ST_GeomFromText(’POINT(1 -1)’); mysql>  SELECT LENGTH(@g); +------------+ | LENGTH(@g) | +------------+ | 25 | +------------+ mysql>  SELECT HEX(@g); +----------------------------------------------------+ | HEX(@g) | +----------------------------------------------------+ | 000000000101000000000000000000F03F000000000000F0BF | +----------------------------------------------------+ 11.4.4 Geometry Well-Formedness and Validity 2060