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# Calculating Distance Between Two Zip Codes

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## Calculating Distance Between Two Zip Codes

Below is a one-pass algorithm for this problem.

Note-1: the point of this program is to show the use of temporary arrays as look-up tables.

>>>---> NOTE-2: <---<<< I do not know the units of the variable Distance.

(The SAS Knowledgebase Note about this problem states the distance is in Miles. Presumably, to obtain the distance in kilometres then the constant 3949.99 needs to be scaled by the proportion of kilometres per mile, or about 1.6 km/mi. The ZIPCITYDISTANCE function in SAS 9.2 may be easier to use.)

These lat/lon values are include in the zipcode table located in SASHELP in any standard SAS installation.

Here is the meat of the article:

Assume the longitude and latitude for the first ZIP code are LONG1 and LAT1, respectively, and the longitude and latitude for the second ZIP code are LONG2 and LAT2, respectively. The Great Circle Distance formula is as follows:

```Dist = 3949.99   * arcos(
sin(lat1) * sin(lat2)
+ cos(lat1) * cos(lat2) * cos(long1 - long2));
```
Note: The Great Circle Distance assumes the earth is a sphere, rather than an ellipsoid. Angles are in radians, rather than degrees.
```*compute-distances-between-two-zipcodes.sas;

/*proc sql;describe table sashelp.zipcode;quit;*/

Data TwoZips;
Zip1 = 30341;Zip2 = 30342;output;
Zip1 = 30343;Zip2 = 30345;output;
Zip1 = 30348;Zip2 = 30311;output;
Zip1 = 30341;Zip2 = 20525;output;

DATA  Distances (keep = Zip1 Zip2 Dist);

attrib Testing length = 4;
retain Testing 1;

*allocate look-up table;
array Latt(99999) _temporary_ (99999*0);
array Long(99999) _temporary_ (99999*0);

*load look-up table;
do until(EndoLoad);
set sashelp.zipcode end = EndoLoad;
Latt(Zip) = Y;
Long(Zip) = X;
end;

if testing then putlog Latt(30341)= Long(30341)=;

do until(EndoFile);
set work.TwoZips end = EndoFile;
Dist = 3949.99
* arcos(sin(  latt(zip1)/57.2958)
*       sin(  latt(zip2)/57.2958)
+       cos(  latt(zip1)/57.2958)
*       cos(  latt(zip2)/57.2958)
*       cos(  long(zip1)/57.2958
- long(zip2)/57.2958
)   );
output;
end;
stop;
run;

PROC Print data = Distances;
run;
```

--macro maven == the radical programmer 11:32, 14 September 2007 (EDT)