 Selecting Local Markets More Accurately With Geocoding
By Brian Carroll, CTO, DirectMail.com
There have been many new advances in computer
technology, allowing for new methods of selecting
address lists geographically. Many database
marketers and list compilers, however, still
restrict their geographical selections to
ZIP Codes,
counties or city names. Often your target market may
be defined by boundaries that do not fall along one
of these entities. Geocoding allows you to convert
postal address data into longitude/latitude
coordinates, enabling a more precise selection.
There are two primary types of geocoding: forward
and reverse. Forward geocoding converts a postal
address into a set of longitude and latitude
coordinates. This is done by comparing the postal
address entered against a vector database/map of a
road network. I'll be focusing on forward
geocoding
in this article, although reverse geocoding is
useful as well.
There are several sources of national vector data
for the road network in the United States. The two
largest commercial sources of such data are
companies Navteq and TeleAtlas, both of which make
their data available for a fee. This is the same
road data that is used for vehicle navigation
solutions such as in-car and handheld GPS units.
There is also free vector data available from the US
Census Bureau in the form of the Tiger/Line Data. A
notable difference between the Tiger Line Data and
the commercial data sources is that it lacks some
attributes, such as one-way street designations,
which are useful for vehicle routing. However, if
our purpose is to locate the longitude and latitude
positions of addresses on a map, it can be quite
useful.
In order to make use of the road network vector
data, to convert addresses into points or the
reverse, you will need a piece of software called a
geocoder. A
geocoder works by parsing apart the
postal address entered into its component parts, and
then looking up those parts against the list of
streets in a given area. For example, it might pull
a list of all streets in the parsed ZIP Code™
component, and then match against the street name.
If a match is found to the street name, it would
then look at the house number and find out how far
down the street the address is and then interpolate
to find the actual position.
Once you have appended the latitude/longitude
coordinates onto a data file, you can then use
spatial querying software to make selections from a
graphical user interface. Being able to select
through the process of drawing a geometric shape is
generally far more precise than being limited to the
traditional means of selection, which are already
present on the postal data, such as ZIP Code, or
carrier route.
You can also combine this selection technique with
demographic fields present on your file to allow for
additional selections. New tools allow for all of
these processes to take place within a simple
user-friendly interface that allows for advanced
data selection by a non-technical user.
---Source: DM News June 11, 2008 newsletter (www.dmnews.com). Brian Carroll is chief technology officer of DirectMail.com. Reach him at bcarroll@directmail.com.
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