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For everyone else, there are ZIP codes. Why do we use them? In , Moon had the idea for a postal zone system that could better sort mail given the staffing shortages created by World War II and increasing reliance on air mail as opposed to the hand-sorting that took place on rail cars.

The first number would represent a group of states, from zero on the east coast to nine on the west coast. The second and third numbers identified the specific mail sorting facility the letter would go to. Later, the USPS added two more numbers to track which post office handled the mail. The most uncertainty usually involves the southern portion of the county, east of the Willamette River, that has a common boundary with Clackamas County along the block of the streets that cross S. Arts Tax: Business Taxes: Most Popular View Less.

Most Recent View Less. Varies Watson Rd. It is bounded on all 4 sides by portions of city streets that each have their own name and addresses. The issue is that census blocks almost always split down the middle of the street.

ZIP codes rarely do because that would require two postal workers delivering mail to that street - one for each side of the street. In the example, one mail carrier may deliver to 3 sides of the block via one ZIP code while another mail carrier delivers mail on the other street in a different ZIP code. When this happens, the Census Bureau will assign the entire block to a single ZCTA in this case, because the census block is the area that is precisely measured.

If you are getting very precise usually a matter of meters, not miles , census block boundaries near the edge of a ZIP code almost always split ZIP codes. The statistics provided by the Census Bureau can give insight into the demographics within the ZIP code. For instance, see our ZIP code rankings. Remember that ZIP codes were made to make mail delivery easier.

They weren't made to correspond to existing boundaries such as cities, counties, or even states. If it is more efficient for a mail carrier to drive across a state line to deliver mail, the ZIP code "boundary" will cross the state lines.

ZIP codes don't usually cross state lines, but some do , , and are good examples. The edges of the boundaries commonly overlap. For the purposes of our free zip code database by county downloads, we will commonly list either the most common region for the ZIP code or list multiple regions if several exist in the ZIP code.

For cities, the assignment is somewhat more complicated. The assignment of cities to ZIP codes is more general. The city is usually the name of the main post office. For instance, almost all ZIP codes in St.