Data types for multi-unit features

Use ST_MultiPoint, ST_MultiLineString, and ST_MultiPolygon to store coordinates that define spaces occupied by features that are made up of multiple units.

Use ST_MultiPoint when you are representing features made up of units whose locations are each referenced by an X coordinate and a Y coordinate. For example, consider a table whose rows represent island chains. The X coordinate and Y coordinate for each island has been identified. If you want the table to include these coordinates and the coordinates for each chain as a whole, define an ST_MultiPoint column to hold these coordinates.
Use ST_MultiLineString when you are representing features made up of linear units, and you want to store the coordinates for the locations of these units and the location of each feature as a whole. For example, consider a table whose rows represent river systems. If you want the table to include coordinates for the locations of the systems and their components, define an ST_MultiLineString column to hold these coordinates.
Use ST_MultiPolygon when you are representing features made up of multi-sided units, and you want to store the coordinates for the locations of these units and the location of each feature as a whole. For example, consider a table whose rows represent rural counties and the farms in each county. If you want the table to include coordinates for the locations of the counties and farms, define an ST_MultiPolygon column to hold these coordinates.

Multi-unit is not meant as a collection of individual entities. Rather, multi-unit refers to an aggregate of the parts that makes up the whole.