怎样在Web.config定义变量值，并且从程序怎么获取值？

Web.config
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
 <appSettings>
  <add key="Location" value="tyfo" />
  <!--add key="Location" value="tyfo" /-->
  <!--add key="Location" value="wlmq" /-->
  <!--add key="Location" value="wuhan" /-->
  <!--add key="Location" value="sjz" /-->
  <!--此数据库连接字符串，不同的地方，数据库连接字符串不一样-->
  <add key="DBConn" value="server=192.168.1.1;Database=****;UID=*****;PWD=******;" />
 </appSettings>
****************************************************************
public static string ConnectionString
{
 get
 {
  switch (System.Configuration.ConfigurationSettings.AppSettings["Location"])
  {
   case "tyfo"://成都本地
    return "server=192.168.1.1;database=*****;uid=******;pwd=******;";
   case "wlmq"://上传到新疆
    return System.Configuration.ConfigurationSettings.AppSettings["DBConn"];
   default:
    return "";
  }
 }
}