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In ASP classic I need to search for the nearest plumbers within a 20 mile radius, given a zip code.

This is a pretty common feature on many websites - like dating or "find a contractor" websites.

You'll enter in your zip code, then you enter in how many miles to "spread out" from this zip code, then the site displays for you all items within a, say, 5 mile radius of your zip code.

So I need to implement this functionality on my website but i have no idea where to start.

I have a database of every zip code in America.

And I have a database of all my plumbers around America

See image:


So when someone goes to my website and types in:

ZIP: 00501 Radius: 5

I need to show them all the plumbers I got within a 5 mile radius of their zip code.

Anyone got any ideas on how I would code that?

Since I have the longitude and latitude of all the zip codes, perhaps i'd have to do some sort of geometric heuristic?

I'm sure this is a classic computer science problem.

But I was only a computer science minor...


little help?

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1 Solution
What database are you using? For example PostgreSQL with the PostGIS geospatial extensions can do all that with the inbuilt function calls. Trying to do something your self would be tricky and most likely slow without a lot of effort at understanding things like how R-tree indexes work.
bobbysdogAuthor Commented:
wow really?

I'm just using MS Access and Classic ASP...
I guess it depends on how big your site needs to be (users, data size, etc). You could code it up yourself fairly quickly with simple geometry functions and if there is only one user that might be acceptable. However, I'm used to catering for 1000s of users so haven't touched Access/ASP in a loooong time :) Just found that MySQL has spatial extensions too if you prefer that to postgresql, but I have never used them.
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bobbysdogAuthor Commented:
ya i would hope the site would eventually have thousands of visits a day.

damn that is a good link you posted...
If you really want that much traffic, get off MS Access immediately :) It will NOT scale.
If you want a very rough procedure (but it might be enoght for your purpose) you can run a query that take into consideration the coordinate of the two Post Code.
Then you can compare them keeping in mind that 1 degree of latitude it's always 69.2 miles.
1 degree of longitude unfortunately can vary with the latitude, but for the whole USA the value is between 48 and 58 (it is basically cos(latidude)*69.2 ) miles.
A couple of comparisson and you are roughly there!
bobbysdogAuthor Commented:
>> "If you really want that much traffic, get off MS Access immediately :) It will NOT scale."

thanks - ya i know Access has its flaws. Unfortunately i'm not smart enough to use anything else. Hopefully, someone will buy my website for a million dollars and then they'll have to worry about optimizing it with a better database later :)

>> "If you want a very rough procedure (but it might be enoght for your purpose) you can run a query that take into consideration the coordinate of the two Post Code..."


i think i follow your procedure. the thing is, there are 40,000 zip codes. So I think i'd need some sort of Spatial Database algo as described above - right?

well, you said:

>> Since I have the longitude and latitude of all the zip codes, ...

so... there you go... that's your Spacial Database
bobbysdogAuthor Commented:

so i have this grid of x y coords

but the point is, I have 40,000 of them.

so the point of this thread is to try to find an algo that will get the 10 nearest points to

33.405559, -86.95141

and to do this in a fraction of a second (so i dont keep the user waiting...) and to implement this in ASP classic and MS Access on a typical windows server

The initilal question was:
how to find the points at less than X miles from 33.405559, -86.95141.

Given the plumbers table done as

and the zips table done as

the resulting query would be:

select plumbers.name,plumbers.ZIP from plumbers inner join zips on zips.ZIP=plumbers.ZIP
where abs(lat-33.405559)< X/55 and abs(lon- (-86.95141))<X/69.2

Open in new window

This query would actually not drow a circle but a square around the given point.

Generally speaking, the original point (the 33.405559, -86.95141) could be found with one first query at the beginning given the "search for" zip, with a simple
select lat,lon from zips where zip=TheGivenZip

Shouldn't take long to run this 2 query
bobbysdogAuthor Commented:

I see what you're getting at.

Ya thats cool. My website does not need to be precise at all. In fact if it guesses with a wide radius thats probably better.

but in your code, it looks like its only getting one side of the point...no?

wouldnt i need something like:

WHERE abs(lat-33.405559) < X/55 AND abs(lat-33.405559) > X/55


abs(lon- (-86.95141)) < X/69.2 AND abs(lon- (-86.95141)) > X/69.2
No, you don't need that, that's the point of having an abs function!
so abs(33.41-33.45) = abs(-0.04) = 0.04
bobbysdogAuthor Commented:

doesnt the abs value of a number just delete the neg sign

so in this case:

abs(lat-33.405559) <  X/55

wouldnt that just give me all the data on top of 33.40

like everything above San Francisco or thereabouts?
imagining X = 6 then X/55 = 0.11
33.5-33.4=0.1  --> abs= 0.1, included
33.3-33.4=-0.1 --> abs= 0.1 included
33.6-33.4=0.2  --> abs= 0.2, excluded
33.2-33.4=-0.2  --> abs= -0.2, excluded

so the formula will give you true for all values between 33.29 and 33.51
bobbysdogAuthor Commented:
oh i think i got it

thanks so much for helping me!!!!!!!!
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