Spatial join

[1] It is similar to the table join operation in relational databases in merging two tables, but each pair of rows is correlated based on some form of matching location rather than a common key value.

[2] It is also similar to vector overlay operations common in GIS software such as Intersect and Union in merging two spatial datasets, but the output does not contain a composite geometry, only merged attributes.

For example, consider the following two tables: When the spatial join is executed, the direction of attachment must be specified, for two reasons: 1) the given spatial predicate may not be commutative, and 2) there is often a many-to-one relationship between the rows (e.g., many students are inside each school district).

Assuming that the districts do not overlap, each student point will be in no more than one school district, so the output would have the same rows as the students table, with the corresponding school attributes attached, as: The reverse operation, in this case attaching the student information to the schools table, is not as simple because many rows must be joined to one row.

Not all software implements this option directly, although in some cases it can be derived through a combination of tools.