Geo-targeting ads on FaceBook requires a bit of homework
Popular social networking site FaceBook offers advertisers the ability to geo target ads. How accurate is the site’s geo-targeting? I think it’s reasonable to say that it is opaqueishly somewhatish accurate.
Let’s have a look at the population and the number of active FaceBook users in Boston and a surrounding group of cities and towns (you pretty much set off World War III if you call a city a town or a town a city in Massachusetts, so I shall refer to all cities and towns as places, the way the United States Census Bureau does).
The table below shows the population for each place according to the 2000 Census. NAFU stands for Number of Active FaceBook Users according to FaceBook’s ad targeting tool (a user is active if he or she has logged into his or her account at least once in the last 30 days). Population refers to the size of the entire population while active FaceBook users are 18 or older.
| Place | Population | NAFU |
|---|---|---|
| Boston | 589,141 | 428,600 |
| Somerville | 77,478 | 7,420 |
| Cambridge | 101,355 | 88,560 |
| Newton | 83,829 | 3,420 |
| Brookline | 57,107 | 36,260 |
| Watertown | 32,986 | 800 |
As you can see, FaceBook’s penetration rate varies wildly according to the site’s geo-targeting tool. It also seem s rather optimistic, especially when one considers that FaceBook claims to reach less than 1.4 million users in a state with less than 6.5 million people.
While it is true that Boston, Cambridge and to a smaller extent Brookline are home to several colleges and universities and house tens of thousands of college students, penetration rates nearing 90% seem a bit unlikely.
Some possible explanations can be gleaned by looking at a collection of places along Interstate Highways 93 and 95 north of Boston:
| Place | Population | NAFU |
|---|---|---|
| Stoneham | 22,219 | 240 |
| Woburn | 37,258 | 50,560 |
| Winchester | 20,810 | 100 |
| Medford | 55,765 | 520 |
| Arlington | 41,144 | 2,240 |
| Burlington | 22,876 | 2,640 |
| Lexington | 30,355 | 2,460 |
| Reading | 23,708 | 240 |
| Wilmington | 21,363 | 620 |
The numbers speak for themselves. Woburn has a penetration rate of some 130% while neighboring Winchester supposedly has hardly any FaceBook users.
What I think is going on is that FaceBook starts with the number of users who specify their location in their profiles, then pad that number using reverse DNS lookups against IP databases. Because of the way the Internet service providers label their access points a town like Woburn has an absurdly large number of users while towns like Stoneham, Winchester and Medford has very small numbers of users. Not only do different ISPs label the location of their users different ways, they sometimes do it differently depending on the access method. For example, while a Verizon DSL subscriber might look up as being in Woburn, even if he isn’t, a Verizon FiOS user in the same place is likely going to be labeled as being in Boston, even though he isn’t.
On top of that, a FaceBook user might well access his or her account regularly from two different towns. In the case of the nine places I list in the table above it would hardly be unusual for a person to live in Wakefield but work in Burlington. It’s quite possible that both places would show up as Woburn in FaceBook’s geo targeting.
The dual access points for a single user probably also help explain why the numbers are so inflated in Boston, Brookline and Cambridge. Yes, I’m suggesting that a substantial number of people check their FaceBook pages while at work (during breaks, no doubt).
Finally, and to reiterate the points made above, behold the numbers for Lawrence and Haverhill, two cities north of Boston, near the New Hampshire border:
| Place | Population | NAFU |
|---|---|---|
| Haverhill | 58,969 | 1,600 |
| Lawrence | 72,043 | 19,380 |
The Haverhill number might actually be more or less correct while the Lawrence number is quite likely inflated the way Woburn’s is.
If you are to geo-target ads on FaceBook you should have a firm understanding of the demographics of the area you’re trying to target and you should play around with FaceBook’s ad tool to figure out the combination of places you should target in order to reach your prospective customers.
Map of Woburn and surrounding towns (Google Maps)
Map of Boston and surrounding areas (Google Maps)
