This functionality don't relate to the RadMap control. It is a built-in functionality of the RadComboBox. You can find the full source code for our examples under your installation path - for example - C:\Program Files\Telerik\RadControls for WPF Q1 2011
Also as a side note - please ask your questions in the forum they are related to - since this is a RadMap related forum your questions about RadComboBox should be in the correspondent thread. This way it will be easier for us to follow the correspondence.
the Telerik team
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