Re: MI-L Distance Calculation

[Cameron Crum]

Could it be that some of the centroids lie outside the 5 mile range even 
though thier "objects" may fall within it? The partially within part of 
your query may be causing this. I would say the first method of using 
the distance function is more accurate if you are concerned with exact 
distances.



Cameron

[EMAIL PROTECTED] wrote:
Group,

I have a question for you regarding distance calculations in MapInfo. I am
trying to find out the best way to determine how many points lie within a
"x" mile radius of a centralized point. I tried to do determine this
information 2 different ways in MapInfo, and received 2 different answers.
Ex.
I have geocodes for where customers originate, and I want to see how many
of them are coming from within 5 miles of my store.
Method 1:
Perform a query (Query1) to determine distance calculation
Distance (Customer_Lon, Customer_Lat, Store_Lon, Store_Lat, "mi")
Then, perform another query on Query1 to get all of the distances <= 5
miles
Method 2:
Select the store and create a concentric ring (actually only create 1 ring
of 5 mile radius).
Press Calculate Ring Statistics button to get the # of geocoded customers
within 5 miles.
(I even included records that were "at least partly within" the ring.)
Does anyone know why these 2 methods yield different results?

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Philip Lesnik
Research Systems Analyst, Market Research
General Growth Properties, Inc.
110 N. Wacker Drive   BSC 3-13
Chicago, IL  60606
312-960-2998
312-960-5519 (fax)
[EMAIL PROTECTED]
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