Posted by LKT/CA on 6/10/08 12:31am
Msg #250611

Zip Code program differences

At www.melissadata.com, mapquest and yahoo maps I enter the same two zip codes - 91786 to 90712

I get two close answers and one far off answer for the distance between those two zips.

Mapquest - 40.95 miles
Yahoo Maps - 41.27 miles
Melissa data - 33 miles

Anyone know why Melissa data's estimate is not close to the other two and how each are calculated? For those not familiar with www.melissadata.com just click on "free lookups" on the right of the screen, then click on the heading "everything zip codes" then click on "distance between zips". TIA

Reply by Lee/AR on 6/10/08 7:15am
Msg #250615

Melissa is as the crow flies. On the others, one is to city center and the other is to the Post Office. Which is which, I don't remember. Melissa is good for getting city names & all zip codes within a city/county.

Reply by PAW on 6/10/08 7:22am
Msg #250616

This is an educated guess on my part. Mapquest and Yahoo (as well as Google) use navigational tools developed for mapping systems. The calculations used are not "line of sight" or straight line calculations but take into account things like terrain and bodies of water. Though they may not use street mapping calculations in zip-to-zip calculations. Melissa may be using direct, straight line calculations, which is always shorter than the others.

Another issue is the location of the "center" of a zip code. Depending on what database is being used, the center point in any given zip code area can vary by a few miles. So going from the center of one zip code to the center of another zip code may be off by as much as 6 or 7 miles, more or less.

Reply by Margaret Paddock on 6/10/08 9:52am
Msg #250638

I live in rural Arizona and I can tell you that I am not at all sure where MapQuest gets its info at times. I know they use the milage from city borders as they do not take into account how far it may actually be into the city itself. I have even had them use street names that do not exist in my town!
I have taken to putting the zip code in my milage book and just have to try to remember the general location of a signing so I can judge the distance. Doing that gives me a better idea of what to charge for the signing and it is a quick and easy way to reference.