.. _zones_network_data_model:

**zones** table structure
=========================

The *zones* table holds information on the Traffic Analysis Zones (TAZs)
in AequilibraE's model.

The **zone_id** field identifies the zone.

The **area** field corresponds to the area of the zone in **km2**.
TAZs' area is automatically updated by triggers.

The **name** fields allows one to identity the zone using a name
or any other description.

.. csv-table:: 
   :header: "Field", "Type", "NULL allowed", "Default Value"
   :widths:    30,     20,         20,          20

   ogc_fid*,INTEGER,YES,
   zone_id,INTEGER,NO,
   area,NUMERIC,YES,
   name,TEXT,YES,
   geometry,MULTIPOLYGON,NO,''


(* - Primary key)



The SQL statement for table and index creation is below.


::

   
   CREATE TABLE 'zones' (ogc_fid    INTEGER PRIMARY KEY,
                         zone_id    INTEGER UNIQUE NOT NULL,
                         area       NUMERIC,
                         "name"     TEXT);
   
   SELECT AddGeometryColumn( 'zones', 'geometry', 4326, 'MULTIPOLYGON', 'XY', 1);
   CREATE UNIQUE INDEX idx_zone ON zones (zone_id);
   SELECT CreateSpatialIndex( 'zones' , 'geometry' );
   INSERT INTO 'attributes_documentation' (name_table, attribute, description) VALUES('zones','zone_id', 'Unique node ID');
   INSERT INTO 'attributes_documentation' (name_table, attribute, description) VALUES('zones','area', 'Area of the zone in km2');
   INSERT INTO 'attributes_documentation' (name_table, attribute, description) VALUES('zones','name', 'Name of the zone, if any');