This is the correct version in order to pass the dropdownlist selectedvalue in the Select attribute of EntityDataSource.
<tr id="SearchDropDown">
<asp:EntityDataSource ID="EntityDataSource1" runat="server"
ConnectionString="name=medicaldb2Entities"
DefaultContainerName="medicaldb2Entities" EnableFlattening="False"
EntitySetName="Medicals" Select="it.[medicalName], it.[city], it.[Region]">
</asp:EntityDataSource>
<td>
<td>
<asp:DropDownList ID="ddlCity" runat="server" AutoPostBack="true"
onselectedindexchanged="ddlCity_SelectedIndexChanged"
DataSourceID="EntityDataSource1" DataTextField="city"
DataValueField="city">
</asp:DropDownList>
</td>
</tr>
</table>
<asp:ListView ID="ListView1" runat="server" DataSourceID="EntityDataSource2">
<LayoutTemplate>
<table>
<tr>
<td>
City
</td>
</tr>
<asp:PlaceHolder ID="ItemPlaceHolder" runat="server"></asp:PlaceHolder>
</table>
</LayoutTemplate>
<ItemTemplate>
<tr>
<td>
<%# Eval("city") %>
</td>
</tr>
</ItemTemplate>
<EmptyDataTemplate>
not found...
</EmptyDataTemplate>
</asp:ListView>
<asp:EntityDataSource ID="EntityDataSource2" runat="server"
ConnectionString="name=medicaldb2Entities"
DefaultContainerName="medicaldb2Entities"
EntitySetName="Medicals"
Select= "it.[MedicalID], it.[medicalName], it.[city], it.[Region], it.[description], it.[Image], it.[adress]"
Where = "it.[city] = @city">
<WhereParameters>
<asp:ControlParameter ControlID="ddlCity" DbType="String"
DefaultValue="2500" Name="city" PropertyName="SelectedValue"
ConvertEmptyStringToNull="true" />
</WhereParameters>
</asp:EntityDataSource>