3 Digit Zip Code Map. You can easily create a 3 Digit Zip Code map using Mapline. The 1st digit of a five-digit ZIP Code represents the division of the USA into 10 large groups of states numbered from 0 (Northeast) to 9 (West). The 2nd and 3rd digits represent the states that are divided into even 10 smaller geographical areas. Also known as “sec center,” they are useful in processing and sorting mails. The US Zip Codes were assigned using the following criteria: Those starting with “0” were assigned to MA, RI, NH.