This section describes the basic concepts of working with a spatial database. In general, once the connection is established with the database, the operation is the same regardless of database.

The currently supported spatial databases are:

Where there are differences in operation among the supported spatial databases, a separate entry will explain how the operation works with each one.

When a connection is established with a spatial database, all queries are handled by the database. That means the software can handle very large queries and very large result sets. If a search is made on the spatial database, the result set is displayed in the Data Browser. As more rows are requested by paging down in the Data Browser, then those rows are sent by the database server.

When operations such as sorting and filtering are performed on the result set in the Data Browser, those operations are actually performed by the database and the results returned to the Data Browser.

This direct connection with the database server lets OpenCities Map handle a very large number of rows quickly and efficiently.

In OpenCities Map, a source can be opened from:

1. The Graphical Source button in the Primary ribbon group located in the Home tab.
   
2. The Graphical Source button in the Database Connection ribbon group located in the Interoperability tab.
   
3. A Graphical Source can also be opened at two locations in the Map Connections dialog as shown:

The following key-ins interact with the Map Connections dialog:

When clicking on one of the locations described above, the Open Connection Parameters dialog opens.

Setting	Description
User	The username used to connect to the database.
Host	The host computer on which the database is running.
Port	The port number for the connection (the default is 5432).
Database	The database running on the selected host computer.
Write Access	Can be set to True or False. The default value is defined in the graphical source during creation. Note: This parameter can only be changed while the user is opening the connection. To change the value of the parameter later, the connection must first be closed and then reopened.
Pessimistic Locking	When set to true, it means that an entity must be locked before it can be edited. Note: This parameter can only be set to false when the connection is established with an Oracle spatial database.
Target Model

Map Connections dialog

Setting	Description
Tree view for connections	The main node is labeled as Connections. Each opened connection is listed, under the main node, using its connection name. The layers of each connection are listed under its name.
Edit Feature Definition	This dialog allows to modify the parameters of an opened connection. However, some parameters can only be assigned when the connection is created and will therefore not be editable in this dialog. As an example, the Write Access setting, in the Connection Parameters" section, is Read Only This is also the case in the Connection Parameters section of the "Map Connections" dialog.
Query Features, Post, Lock Features, Unlock Features, Discard Changes, and Erase Cached Instances	You can now select the layers you wish to work with. You can make selections in all opened connections. The different options Apply Where Clause, Continue on Error, Refresh Features, Refresh Local Instances and Retain Locks are applied to all connections.

Note: When no connection is open the message center will display the message, No Active Connection.

When one or more connections are open based on the tool selected you can expect the following behavior:

Connection Tools	Description
New Connection	Let you create new connections while other connections are still active.
Open Connection	You can open a new connection while other connections are still active.
Save, Save As, Edit Feature Definitions, Select Oracle Version	If no connection is selected in the Connections section of the dialog: The message " One connection must be selected to use this tool" is displayed in the message center. If more than one connection is selected, or if the main node is selected: The message "Only one connection must be selected to use this tool" is displayed in the message center.
Remove Connections, Refresh Dynamic Domain Lists	If there is no connection selected in the Connections section of the dialog: The message "One connection must be selected to use this tool " is displayed in the message center. If more than one connection is selected, or if the main node is selected: The tool is executed on all selected connections. The message "Do you really want to remove all selected connections?" is displayed in the message center.

Spatial Tools	Description
Query, Post, Lock, Unlock, Discard and Erase	Same as the tools available in the ribbon. These tools are independent of the connection selected.