Hi Tracy,

Not sure if of any help, but you may want to check this link also
http://blogs.lessthandot.com/index.php/DataMgmt/DataDesign/sql-server-zipcode-latitude-longitude-pr

>Or maybe the Haversine Formula? Which? In VFP, If I have two coordinates on a map with x/y for 0/0 like the examples below and a radius to draw a circle around that position (let's say 500 ft), how can I tell if any other x/y coordinates are within the radius? I know I need to check and see if the distance to the 2nd x/y coordinates is less than the radius, but it escapes me -- math in general tonight. I've tried checking within the radius, just returning the distance in feet, but just cannot get it right....
>
>None of these are accurate--the distance should be about 392 ft (a mish-mash of attempts from me, the web, etc):
>

>*circumference is 360 degrees times 60 minutes/degree times 1.852 km/minute = 40003.2 km. 
>*The implied radius is the circumference divided by 2 pi: R = 6367 km = 3956 mi 
>lon1=  1698101.25   &&1713881.3750
> lat1=   813831.69 && 833601.8125
>lon2 =    1698215.13 &&1697432.8750
>lat2 =    813458.25 && 810161.0625
> R = 3956 && 3963 && 3956
> dlon = lon2 - lon1
>  dlat = lat2 - lat1
>  a = (sin(dlat/2))^2 + cos(lat1) * cos(lat2) * (sin(dlon/2))^2
>  ? a
>  c = 2 * atn2(sqrt(a), sqrt(1-a)) 
>  ? c
>  d = R * c
>  ?[Example1: ]
>  ??d
>
>   
>*--is point within a radius
>radius = 500  &&(what would 500 ft be?)
>centerx =  1698101.25   &&1713881.3750
>centery =   813831.69 && 833601.8125
>x =    1698215.13 &&1697432.8750
>y =    813458.25 && 810161.0625
>
>?[Example2: ] 
>?? (x-centerx)^2 + (y - centery)^2 
>?[     Inside radius: ] 
>?? (x-centerx)^2 + (y - centery)^2 < radius^2
>
>
>
>*--Get distance between two points
>#DEFINE KMRAD 6377
>#DEFINE MIRAD 3956 && 3963  
>#DEFINE RADIANS DTOR
>
>
>tlKM = .F.
>
>lon1=  1698101.25   &&1713881.3750
>lat1=   813831.69 && 833601.8125
>lon2 =    1698215.13 &&1697432.8750
>lat2 =    813458.25 && 810161.0625
>
>    lnDistance=IIF(tlKM, KMRAD, MIRAD)*;
>     ACOS(COS(DTOR(90-lat1))*COS(DTOR(90-lat2))+;
>     SIN(DTOR(90-lat1))*SIN(DTOR(90-lat2))*;
>     COS(DTOR(lon1 - lon2)))
>
>?[Example3: ]
>??lnDistance  && *5280 && 5280 feet in a mile
>
>
>
>*--Select all within the radius  &&Courtesy Carl Karsten 
>#DEFINE cdbl
>#DEFINE _PI 3.1415926535893
>#DEFINE _StatuteMile 5280 &&' 5280 feet = 1 statute mile
>#DEFINE _NauticalMile 6076.11549 &&' 6076.11549 feet = 1 nautical mile
>#DEFINE _Seconds 60 && ' 60 seconds = 1 nautical mile
>lon1=  1698101.25   &&1713881.3750
>lat1=   813831.69 && 833601.8125
>lon2 =    1698215.13 &&1697432.8750
>lat2 =    813458.25 && 810161.0625
>
>? InRadius(lat1,lon1,500,lat2,lon2)
>return
>
>FUNCTION InRadius( tlat, tlong, tnRadius, tlat2, tlong2 )
>    LOCAL lnResults, lnSeconds, ;
>      lnLatRange, lnLonRange,;
>      lnLowLat, lnLowLon, ;
>      lnHighLat, lnHighLon
>      
>   *' 1 degree of latitude = 60 nautical miles or 1 minute = 1 nautical mile
>    lnLatRange = tnRadius / ((_NauticalMile / _StatuteMile) * _Seconds)
>
>    *  Longitude is a bit more complicated; 
>    * 1 degree of longitude at the equator = 60 nautical miles, 
>    * At the poles 1 degree = 0 nautical miles.
>    lnLonRange = tnRadius / (((COS(cdbl(tlat * _PI / 180)) * ;
>				_NauticalMile) / _StatuteMile) * _Seconds)
>
>    lnLowLat = tlat - lnLatRange
>    lnHighLat = tlat + lnLatRange
>    lnLowLon = tlong - lnLonRange
>    lnHighLon = tlong+ lnLonRange
>
>?[Example4: ]
>?? tlat2 <= lnHighLat;
>      AND tlat2 >= lnLowLat;
>      AND tlong2 >= lnLowLon;
>      AND tlong2 <= lnHighLon
>?[Example5: ] 
>?? getdistance2(lon1,lat1,lon2,lat2)
>
>RETURN
>
>      
>FUNCTION getdistance2  &&Courtesy Carl Karsten
>LPARAMETERS lon1,lat1,lon2,lat2
>
>*--Get distance between two points
>#DEFINE KMRAD 6377
>#DEFINE MIRAD 3956 && 3963  
>#DEFINE RADIANS DTOR
>
>
>tlKM = .F.
>
>lon1=  1698101.25   &&1713881.3750
>lat1=   813831.69 && 833601.8125
>lon2 =    1698215.13 &&1697432.8750
>lat2 =    813458.25 && 810161.0625
>
>    lnDistance=IIF(tlKM, KMRAD, MIRAD)*;
>     ACOS(COS(DTOR(90-lat1))*COS(DTOR(90-lat2))+;
>     SIN(DTOR(90-lat1))*SIN(DTOR(90-lat2))*;
>     COS(DTOR(lon1 - lon2)))
>
>?[Example6: ]
>??lnDistance  
>
>return lndistance
>
>

>
>I'm brain dead! I've mucked it all up.....