Find Counties in area

We have the need to determine surrounding counties of a particular county.

For example how can I determine, if I entered a zip code for Contra Costa and the property is also right on the line of alameda that Alameda is a neighboring county of Contra Costa

Could it be determined by the longitude and latitude of the zip code in comparison with the counties?

Hello,

Although I'm sure a geospacial co-ordinate system could be used to determine this, most people think it overkill and just use a proximity table :)

tCounty (CountyID int, CountyName varchar)

tCountyAdjoined(CountyID int FK to tCounty.CountyID, AdjoiningCountyID int FK to tCounty.CountyID)

So if Contra Costa was near Alameda, tCountry might contain rows:

1, Contra Costa

2, Alameda

And tCountyAdjoined would contain:

1, 2

Obviously, a simple join then returns all counties that adjoin a particular County.

Unfortunatly, you'll need to manually determine and input the proximity values (unless your postal service supplies these details as in Australia.)

Cheers,

Rob