2/17/2012 Telephone Area Codes

I recently found myself dealing with Telephone Area Codes. “Area Codes” are levels of geography that have been defined by the telephone industry over the years, with new area codes being added (and old ones being adjusted) as a result of population and commercial growth. There are currently 281 Area Codes in the United States. They range from single-Area Code states [Alaska (907), District of Columbia (202), Delaware (302), Hawaii (808), Idaho (208), Maine (207), Montana (406), North Dakota (701), New Hampshire (603), Rhode Island (401), South Dakota (605), Vermont (802), and Wyoming (307)] to multiple-Area Code states [the largest being California (29), Florida (17), New York (14), and Texas (23)].

The purpose of dealing with Area Codes is that you would like to get insight into a customer (the demographics of the area associated with the customer), but the only data point you have is a telephone number. Although they began with a simple definition covering specific areas (New York City = 212, Chicago = 312, etc.) and evolved to nationwide seamless coverage, they have now become, in some regions, overlaid on top of each other (although Area Code 657 covers 10 cities in California, Area Code 714 also covers those 10 cities, plus an additional 64 cities). For those interested, Wikipedia has an excellent article on the North American Numbering Plan
http://en.wikipedia.org/wiki/North_American_Numbering_Plan

Note: although the Wikipedia article lists 323 Area Codes, it includes proposed Area Codes and overlays; I am using the USA Telephone Area Codes boundary file available from Esri (281 Area Codes):


And don’t get me started on Area Codes for cell phones! My understanding is that the area code is assigned at the location where the cell phone is purchased; but by their very nature, these are mobile devices. My only hope for “data integrity” (that the cell phone Area Code actually means a location) is that, in these economic times, less people are moving. It was reported in November 2011 that only 11.6% — 35 million people — changed residence from 2010 to 2011, the lowest rate since the Census Bureau began collecting the statistics in 1948. In the mid-1980s, more than 20% were moving each year.

Analysis

Analysis is relatively straightforward – identify the area you are interested in, and grab (if at the state-level), or roll-up, the demographic variables you want. Originally, I wanted to do something complicated, like California. But after getting my hands (very) dirty, I will focus instead on the 12 Area Codes in Connecticut, Massachusetts, and Rhode Island:


By definition, Area Codes 339, 351, 774, and 857 are overlays of 781, 978, 508, and 617, respectively, so demographics need to be calculated for 8 Area Codes. 401 is all of Rhode Island, so that is an “easy grab”.

Examining Boundary files, it is apparent that Area Codes in Connecticut and Massachusetts are defined by Census Subdivision (“Cities and Towns”), and not Counties. The County Subdivision files for TIGER2010 can be downloaded from the Census Bureau’s ftp site:
ftp://ftp2.census.gov/geo/tiger/TIGER2010/COUSUB/2010/

From the Census Bureau web site, download Report DP03 – Selected Economic Characteristics [2006-2010 American Community Survey 5-Year Estimates] for the County Subdivisions in Connecticut and Massachusetts. Of the 173 Census Subdivisions in Connecticut, 51 are in Area Code 203 (and the rest are in 860) (for the record, the 351 Massachusetts Subdivisions are distributed: 98 in Area Code 413, 112 in 508, 12 in 617, 50 in 781, and 79 in 978). There are dozens of variables that can be rolled-up, but the ones I like are

VC74 VC85 VC101 VC112 VC156 . Count of Total Households Median Household Income Count of Total Families Median Family Income Percentage of Families and People whose Income in the past 12 months is Below the Poverty Level

State/ Area_Code CT/203 CT/860 MA/413 MA/508 MA/617 MA/781 MA/978 RI/401 Total Households 666,967 692,251 320,464 767,523 485,987 465,413 473,165 410,305 Median Household Income $76,757 $67,850 $51,767 $67,416 $61,649 $79,943 $73,820 $54,902 Total Families 450,477 461,176 200,102 518,507 245,397 311,787 324,795 285,572 Median Family Income $95,507 $82,703 $66,018 $82,875 $77,900 $99,032 $90,383 $70,663 Percent Below Poverty 6.7% 6.2% 10.6% 6.4% 11.5% 5.1% 6.3% 8.4%

These numbers illustrate that there are very wide ranges in income levels and poverty levels between Area Codes, even here in relatively-homogeneous Southern New England. I look forward to completing this analysis for the rest of the United States.