2f_attributes.adoc

Attributes

Introduction

Non-spatial attribute data are entities (e.g., tuples or rows) of observations that may not have an explicit geometry property. In GeoPackage, this data is stored in user-defined attribute tables. These tables may contain properties such as an ID or geo-locatable address that allow them to be relationally linkable to rows in other attribute, feature or tile tables.

Examples of attribute data include:

• meteorological readings from a weather station

• flow readings from a stream gauge

• traffic volumes from embedded highway sensors

• lists of customers

• delivery stops

• work orders

Contents

Data

Contents Table - Attributes Row

Requirement 118

The gpkg_contents table SHALL contain a row with a data_type column value of "attributes" for each attributes data table or view.

Attributes User Data Tables

Data

Table Definition

Non-spatial attribute data is stored in user-defined Attribute tables. Attribute sets are rows in an Attribute table. The attributes are columns in a Attribute table. (A GeoPackage is not required to contain any Attribute data tables. Attribute data tables in a GeoPackage may be empty.)

Requirement 119

A GeoPackage MAY contain tables containing attribute sets. Every such attribute table SHALL be structured consistently with Table 1 and [example_attributes_table_sql]. A table SHALL have a primary key column of type INTEGER and that column SHALL act as a rowid alias.

Note	The integer primary key of an attributes table allows features to be linked to row level metadata records in the gpkg_metadata table by rowid [B5] values in the gpkg_metadata_reference table as described in clause [_metadata_reference_table] below.

Requirement 151

A GeoPackage MAY contain views containing attributes. Every such attributes view SHALL have a first column of type INTEGER and that column SHALL contain unique values for each row.

Note	Since the concept of primary keys does not exist for views in SQLite, this requirement provides a way to produce a compliant attributes view with a discoverable key-like column[K17].

Table 1. Sample Attributes Table Definition

Column Name	Col Type	Column Description	Null	Key
id	INTEGER	Autoincrement[K6a] primary key	N/A[K6b]	PK
text_attribute	TEXT	Text attribute of feature	yes
real_attribute	REAL	Real attribute of feature	yes
boolean_attribute	BOOLEAN	Boolean attribute of feature	yes
raster_or_photo	BLOB	Photo of the area	yes