Select data field to display in dropdownlist (Id Control)

You need to use Cascading dropdownlist concept here. Means first you need to all records into Region dropdown then onselect of dropdown it will fetch id of region and filter all cities which are belong region(RegionID).Please follow below links that may help you:

 

http://www.aspsnippets.com/Articles/Populate-Cascading-DropDownList-from-Database-in-ASPNet-Example.aspx

 

http://www.aspdotnet-suresh.com/2012/11/country-state-city-cascading.html

 

http://www.codeproject.com/Articles/32725/Using-CascadingDropDown-with-a-Database