An MSD radix sort would be more efficient than the LSD sort when the numbers form some type of "sorting" index. For example, zip codes are arranged by geographic areas such that the first digit typically identifies a particular region. Each additional digit serves to futher identify the location. By sorting on the most significant digit the post office is able to deliver the mail more efficiently. Similar examples can be found in telephone numbers and school rosters. In the case of telephone numbers the area codes identify regions of the country, and the first three digits of the local phone number identify particular areas of a city. Similarly, roster numbers for a schedule of courses are usually arranged so that the roster number roughly coincides with the alphabetized course schedule. For example Computer Science 101 appears before Computer Science 211, and Art 300 appears before English 101. Sorting by the MSD would be more useful in these cases.