CDXZipStream supports a variety of distance formulas including CDXDistance, CDXRouteMP and CDXDistance2WP.  Each is optimized for different situations and involves varying times to calculate.  

CDXDistance is used to calculate straight-line distance between zip codes.  You simply reference two zip codes and the CDXDistance formula returns the distance in either miles or kilometers.  The custom formula calls our custom database to return latitude and longitude for the zip code, and the distance calculation is performed based on this data.  It is relatively fast and should be used where the central location of a zip code can be used to approximate distance between locations.

If you need driving distance or time you will need to use CDXRouteMP, which works in conjunction with the desktop version of Microsoft MapPoint.  The calculation times for this are relatively slow at about 1 second per route, with more complex routes taking more time.  If you are going to make thousands of calculations you should dedicate your PC to this during off hours or run this on a separate machine.

The fastest calculation is CDXDistance2WP, which uses latitude/longitude pairs to perform straight line distance calculation. You can geocode a list of addresses and then use this function to calculate exact distances.  We recommend this when trying to analyze long address lists.

A typical task may require calculating driving time or distance for a large matrix of addresses or zip codes.  For instance, it may be necessary to determine which customers in a list of thousands are within a one hour driving time of multiple store locations.  The best way to handle this is a two-step process.  First, we can get the latitude and longitude of each customer address and use CDXDistance2WP to calculate the straight-line distance from each store.  Then we can filter this list for customers that are within 100 miles of each store, and use CDXRouteMP to get the exact driving time for this smaller list.  Using a combination of distance calculations in this case allows for fairly fast analysis of very large data sets, without sacrificing accuracy

Demographic data as provided in our products CDXZipStream and CDXStreamer is based on various census geographies.  But what do we really mean here by "geography"?  It's really just the way the U.S. Census defines a geographic area in the United States, and many census geographies, such as states and counties, we're already pretty familiar with.  However, have you ever heard of a Census Designated Place, or CDP?  How about a Core-Based Statistical Area, or CBSA?  If you're interested in using demographic data to find a location for your business, design a marketing program, or even perform academic research, you may find these less well-known geographies useful.

The most basic census geography is the census block, which is well-named since it is the building block for just about all other geographies.  For the 2010 census there are over 11 million census blocks covering the U.S., the District of Columbia, and Puerto Rico.  Since it is the smallest geography, census blocks can be grouped together to form larger geographies such as counties, states, and regions.  Here's a helpful diagram provided by the Census Bureau, with the smallest geographies at the bottom, and the largest geographies at the top:

Census blocks are typically defined by physical features like roads or rivers, and other boundaries such as city limits or property lines.  They can correspond to individual city blocks, but in rural areas may cover much larger areas.  Population is also a factor; the average size nationally of a census block is about 100 people.

Here are some other census-specific geographies of interest:

Census tracts are geographic units representing urban or rural neighborhood-like communities, and are made up of adjoining census blocks.  Census tracts, like blocks, usually coincide with the limits of cities, towns or other administrative areas, and several tracts commonly exist within a county. There are just over 66,000 census tracts covering the U.S., with an average population of about 4,000.  Census tracts can be extremely useful for demographic analysis since they are fairly stable, well-defined entities that are large enough to get statistically-significant data, but small enough to see a unique picture of the community.

Places are a catch-all geography that lumps together a wide variety of communities such as cities, towns, boroughs, townships, villages, and municipalities. This category also includes CDP's  (Census Designated Places) which are populated communities that do not have a local government and are not incorporated. Examples include small rural areas and unincoporated retirement communities.  Using census data for "places" can be particularly useful for smaller communities where the population is fairly homogenous, but for large cities such as New York, demographics by place can provide only a limited picture of a very diverse population.

Core-Based Statistical Areas are urban areas with a population of at least 10,000. CBSA's are defined by the U.S. Office of Management and Budget, and are determined more by social and economic ties within an area, rather than physical or political boundaries.  As a result, they can cover multiple counties, cities, and even states.  There are currently 955 CBSA's in the U.S., which are grouped according to population.  An area with a population between 10,000 and 50,000 is a Micropolitan Statistical Area, and an area with a population greater than 50,000 is a Metropolitan Statistical Area.   Since CBSA's are a truly functional geography that reflect where people live and work, they can provide a very unique demographic perspective on the area.

Zip Code Tabulation Areas, or ZCTA's, are the Census Bureau's version of zip codes, and were first developed for tabulating Census 2000 data.  ZCTA's approximate zip code areas by aggregating census blocks.  But since zip  codes as defined by the U.S. Postal Service are ever-changing and do not follow census boundaries, there will always be some discrepencies between the two.  ZCTA's of course are extremely useful since they can easily be linked to a mailing address, but it should be recognized that ZCTA's and zip codes are not exactly the same thing.  One of our recent blog posts reviews ZCTA's in more detail.

For more information about census geographies, here are some good resources:

Reference Resources for Understanding Census Bureau Geography

Census Bureau Geography

Metropolitan and Micropolitan Statistical Areas

Zip Code Tabulation Areas

In a previous post we talked about how the results of the 5-year (2005-2009) American Community Survey, released in December 2010, would provide demographics down to the zip code level for the first time.  Unfortunately, the Census Bureau did not provide zip code data with the current data release, and won't be including it for some time, at least until 2012-2013.

Zip codes, as defined by the U.S. Postal Service, are not actually a "geography" included in Census Bureau surveys.  Realizing there is significant interest in zip code demographics, the Census Bureau did provide Census 2000 data by "ZCTA" (Zip Code Tabulation Area), which required grouping data from small census "blocks" in order to approximate an actual zip code.  You can see how ZCTA's and zip codes compare in these example maps of Washington state. (Also see our previous blog post with a more detailed ZCTA description.)

Since zip codes frequently change in definition and area, the Census Bureau must now update ten-year old ZCTA definitions.  This is a complex task that was not completed in time for this first 5-year data release.  In the meantime, we at CDX Technologies are evaluating other options for providing ACS data in smaller geographies.  (We currently provide state, county, CBSA (Core-Based Statistical Area) and city data in our CDXZipStream ACS data feed.)  We'll keep you posted as our work proceeds.