Could you post the correct code instead please, as this code will not compile? I would rewrite this to look like this instead:
string uri = string.Format("~/OutdoorMedia.aspx?LocationId={0}&TypeId={1}" ,
HttpUtility.UrlEncode(DropDownListLocation.SelectedValue),
HttpUtility.UrlEncode(DropDownListType.SelectedValue));
Response.Redirect(uri);
You can then set a breakpoint on your Response.Redirect and see what the value in uri is.