Why are a mailing address and a street address required?
For many libraries the information is the same, but some libraries still have post office boxes or receive mail somewhere other than where the library is located. A street address is needed for shipping purposes (most carriers will not deliver to post office boxes), or it is used for mapping purposes. More data is becoming available electronically to track census information by having a physical location. The last four digits of the zip code (the zip extension) can identify which side of the street your library is on. If you are unsure about what the zip extension for your library is, go to http://zip4.usps.com/zip4/welcome.jsp. Many libraries have their very own specific zip extensions that are different than the other addresses on the same street. The correct extension will expedite your mail.
