To connect to an Access database from AutoCAD Map 3D, set up an ODBC connection for that database using a control panel in Windows. Then, connect to this source using Data Connect, just as you connected to the physical data sources in your map. The database source contains a field that you can match to a property in the Parcels layer, so you can join the data to the parcels. Using the combined data, you create a calculated property that is stored in the map but is not saved back to the original data stores. This property is not available in either original data source alone. It requires a join and a calculation to create it.