||ZIP Codes and
carrier routes are technically not areas.
||ZIP Codes and
carrier routes are simply collections of addresses.
||Since they are
not areas, official ZIP Code or carrier route boundaries
do not exist.
ZIP Codes and carrier routes are often treated as geographical
||Over time, ZIP
Codes and carrier routes become fragmented and intermingled.
||As a result of
the fragmentation, ZIP Code boundaries are fuzzy.
coverage areas (and thus directory scoping) are changing all the
fragmentation of carrier routes hinders delivery quality.
Compare Grid Mapping
with Postal Carrier Routes
Improvement Plan) are Not Zones and Carrier
Routes are Not Routes
Neither ZIP Codes
nor postal carrier routes are area or line
geographies. Both ZIP Codes and mail
carrier routes are collections of
addresses. Historically, a ZIP Code is the
collection of addresses served by a
particular Post Office branch while a
carrier route is merely the collection of
addresses served each day by the same mail
Everyone Treats Them As Areas
When ZIP Codes
and carrier routes were originally designed,
the delivery points they served were
typically well organized and bunched
together - thus many people treated them as
areas. The US Postal Service also
unwittingly encouraged the concept of ZIP
Codes and carrier routes as geographies by
their naming. ZIP is short for Zone
Improvement Plan yet ZIP Codes are not
zones. A zone is a two-dimensional area yet
addresses are points and points have no
The usage of ZIP
Codes as areas has a lot to do with the fact
that there are few alternatives. Counties
are too large for most purposes. Census
tracts and block groups would be perfect but
Census naming schemes are too cumbersome.
More importantly, everyone knows what their
ZIP Code is because ZIP Codes are a critical
component of their mailing addresses. Hardly
anyone can name their own Census tract and
The concept of
ZIP Codes as points rather than areas is
dramatized by the fact that some ZIP Codes
consist of a single delivery point. A large
business may have its own ZIP Code. A large
office building may include more than one
ZIP Code. Naval ships often have their own
From Order to
Chaos: How Carrier Routes Become Fragmented
When new homes and businesses are built
along a mail carrier's route, the time
required to deliver that route obviously increases.
To minimize overtime labor costs, the US
Postal Service must reallocate parts of
carrier routes to other mail carriers.
Imagine starting with a hundred mail
carriers for a hypothetical community.
Within a few years, population growth
could cause the time required to deliver
each route to increase significantly. To
minimize overtime, parts of each of those
routes are then re-assigned to new carriers.
Thus what started as 100 relatively congruent
routes then become 100 routes plus 100
additional pieces of routes. What once
started as rather simple, efficient routes
becomes, over time, much more complex and
For US Postal
Service mail carriers, the fragmentation of
carrier routes isn't as problematic since
carriers deliver the same route day after
day after day. No
matter how complex and fragmented their
routes become, postal workers quickly adapt
from sheer repetition. For a directory
delivery worker that delivers the route
once per year instead of every day of the
year, however, the fragmented route is a much bigger
The fragmentation of postal carrier routes
is problematic for directory distribution.
carrier routes are notorious for being
In the carrier route map on the left,
notice how the carrier route shown in light green is in 7
In contrast, grid-based delivery zones - like those shown on the
right - are usually in one piece. One piece
means less errors.
Directory Delivery Problems Common to Carrier
Since ZIP Codes
are collections of carrier routes, ZIP Code
boundaries also become increasingly complex
and less defined over time. Remember, the Post
Office is only concerned with addresses
which are points. A critical ramification of
ZIP Codes as points rather than areas is
that the Postal Service does not bother to
publish ZIP Code boundaries. Nevertheless,
since lots of people consider ZIP
Codes as convenient forms of area geography,
there are mapping companies that attempt to
define suitable boundaries. Different mapping
companies, however, may define very
different boundaries for the same ZIP code.
The ZIP Code on the left is the SAME
ZIP Code on the right. The
difference illustrates how two
mapping companies may define
different boundaries for the same
In this particular case, the
variance in boundaries is of little
or no significance because the
population (shown as red dots on the
right) is concentrated in central
areas common to both boundary
world application for publishers:
discussing delivery areas with your
distribution vendors, be aware that ZIP
Codes are constantly being changed by the
Post Office. Their service areas change. ZIP
Codes are often split and new ZIP Codes
created. The ZIP Code boundaries shown
on a map printed three years ago may vary
significantly with the current boundaries.
Furthermore, different mapping companies may
show radically different boundaries for the
exact same ZIP Code. For confirming
can provide current ZIP Code, ZCTA, and
other boundary maps.
USPS sometimes create new ZIP Codes
by splitting existing ZIP Codes.
Entire ZIP Codes have been known not
to receive directories because a
publisher's directory scoping did
not reflect current ZIP Code
time, ZIP Code and carrier route
delivery points have a tendency to become scattered
and intermingled as specific addresses are
allocated and re-allocated to
different mail carriers. The
"boundaries" become increasingly obscured.
Other factors also contribute to the
fragmentation of carrier routes.
Streets sometimes become
one-way roads, for example, and new growth
requires the building of additional post
offices with their own carrier routes.
points on the right are the locations of real
addresses. The colors of the dots
indicate their current ZIP Codes.
create ZIP Code boundaries, a
mapping company would prefer to draw
boundaries such that all the
addresses are segregated by ZIP
Code. To do so, however, would often
produce boundaries that are
impractical - especially given the
layout of the area's road network
and the resolution at which the map
will be printed or displayed.
overly complex boundaries - and to
conform to local road locations -
the mapping company will have to
make compromises. Invariably, some
addresses will be located in the
wrong ZIP Code area.
fuzzy boundaries often explain why
some homes and residences in a ZIP
Code may get books while next door
neighbor do not receive books.