Practical GIS

WKT is short for Well-Known Text, while WKB is the abbreviation of Well-Known Binary. They are the ASCII and binary representations of the same format, mainly used by spatial extensions of (O)RDBMS software (such as PostGIS). They support 2D geometries and introduce some special types besides the simple ones (for example, curve, TIN, surface, and others). We can come across WKT representations of geometries mainly in official PostGIS and QGIS examples, as both like to use it. A WKT representation of a point looks like the following:

    POINT (17.80554 46.04865)

The format is rarely used with files (it cannot even represent attributes), however, it is a very common format to communicate geometries to SQL-based software. There are extended versions of these formats called EWKT and EWKB, which were created by the team behind PostGIS, and are mainly used in it. It extends WKT and WKB by standardizing geometries in higher dimensions (up to four).

Vector geometries in GIS usually can take up four dimensions. They are called X, Y, Z, and M. The first three are unambiguous, while the fourth is usually called the measure coordinate. For example, in a 3D river streamline, the first three coordinates represent the vertices in 3D space, while the M coordinate can be used to store river kilometers (or river miles), the distance from the mouth along the river.

Table of Contents for Practical GIS

Table of Contents for
Practical GIS