cartodb-postgresql/doc/CDB_Overviews.md

Overviews are tables that represent a reduced version of a dataset intended for efficient rendering at certain zoom levels while preserving the general visual appearance of the complete dataset.

The reduction consists in a fewer number of records (while each overview record may represent an aggregation of multiple records) and/or simplified record geometries.

Overviews are created through the CDB_CreateOverviews.

The CDB_Overviews function can be used determine what overview tables exist for a given dataset table and which zoom levels correspond tt

CDB_CreateOverviews

Create overviews for vector dataset.

Using the function

The table for which overviews will be generated should be a Cartodbfied dataset with vector geometry.

SELECT CDB_CreateOverviews('table_name');
--- Generates overview tables for the dataset

Arguments

CDB_CreateOverviews(table_name, ref_z_strategy, reduction_strategy)

• table_name regclass, table for which overviews will be generated
• ref_z_strategy regproc, function that provides the Z-scale strategy. It returns the base Z level for the dataset. It should have these arguments:
  • table_name regclass, table to compute the reference Z scale for
• reduction_strategy regproc, function that provides the reduction strategy to generate an overview table from a table for a smaller scale (higher Z number). It returns the name of the generated table. It should have these arguments:
  • base_table_name regclass, base table to be reduced.
  • base_z integer, base Z level assigned to the base table.
  • overview_z integer, Z level for which to generate the overview.

CDB_Overviews

Obtain overview metadata for a given table (existing overviews)

SELECT CDB_Overviews('table_name');
--- Return existing overview Z levels and corresponding tables

Arguments

CDB_Overviews(table_name)

• table_name regclass, table for which overviews will be generated