Defining a Join

In the following example, Hydrants and Watermains both have a WmainID property which will be used to create the join.

Select the feature on which the join is to be created and select Join from the context menu.

The Join interface lists all the features available in the session. The left side will be set to the feature selected from the Map Manager. A different feature can be selected by using the pulldown list.

From the combo-box, select a property for the left side of the join.

On the right is a similar list of features, currently known to the OpenCities Map session. To create a join, select a property from a feature on either side and select Add Selected Left/Right Properties. To create a join, the data types of both selected properties must be identical.

Note: For spatial graphical sources joins are performed at the database level for performance improvements. When working with feature classes from spatial graphical sources, joins cannot be made from a left side feature class to a right side class that is not in the same graphical source.

To remove the join, select Remove Selected Joined Properties.

Other features can be added by selecting the New Sources button.

Only features that can be valid OpenCities Map feature types are supported. This includes all supported GIS types and Oracle Spatial tables. Data sources such as CSV files can be defined as VRT files and loaded in the Joins dialog.

Database tables must have a primary key to be listed for the Join operation. In the case of views without primary keys, one can be defined using the following statement

Oracle: alter view cola_view add primary key (mslink) disable;

Once the join has been created, the properties from the joined feature (right side feature) will be displayed whenever the properties from the selected feature (left side feature) are accessed. If there is more than one feature that meets the criteria, as in a one to many relationship, then only the first queried feature properties will be displayed.

Hydrant feature before a join to the Watermain feature:

After the join, the Watermain properties are available when reviewing the Hydrant features.

The properties are also available in the Data Browser and can be used as any property of the feature. However, they are read-only properties as shown by the faded display.

Finally, the joined properties are available when exporting to any of the supported GIS formats.