so going by lat and long makes more sense, thx
Yes, like Ben said it's complex. But there are off-the-shelf apps to do it for you. What we did (at my last gig) was keep the original address and the standardized address for each record. Match on standardized for dupes, and show a person the matches.
We were checking one-by-one in real time to see if we had done work on a property before, but you could easily do this for a large set and query for dupes to get a sense of scale. The package we had also had an optional web service to check whether the standardized address was recognized by the USPS.
Checking for lat/lon is just an abstracted version of this process. The advantage of using addresses is that looking at what comes out the other end as "standardized" is human-verifiable.
