Working Example From one of my Applications... You will need to remap the columns and tables obviously.
DECLARE @Lat float= -83.555
DECLARE @Long float = 43.555
SELECT TOP 100 ID, Abbr, Distance FROM
(
SELECT NL.NodeLocationID AS ID, NL.NodeLocationAbbr AS Abbr, (ABS(NL.Latitude - @Lat) + ABS(NL.Longitude - @Long)) / 2 AS Distance
FROM NodeLocations AS NL
WHERE (NL.Latitude IS NOT NULL) AND (NL.Longitude IS NOT NULL)
) AS D1
ORDER BY Distance
The below finds the closest items relative to other items in the same table (can be altered by changing NL2 to another table). This works to find the closest items, however performance is horrid depending on how many records your dealing with. I would suggest you create a static field and calculate each one via a background process.
SELECT *
FROM
(
SELECT TOP 100 PERCENT *
, ROW_NUMBER () OVER (PARTITION BY ID ORDER BY Distance ASC) AS Rnk
FROM
(
SELECT NL.NodeLocationID AS ID, NL.NodeLocationAbbr AS Abbr
, NL2.NodeLocationID AS ID2, NL2.NodeLocationAbbr AS Abbr2
, (ABS(NL.Latitude - NL2.Latitude) + ABS(NL.Longitude - NL2.Longitude)) / 2 AS Distance
FROM NodeLocations AS NL
JOIN NodeLocations AS NL2 ON NL.NodeLocationID<>NL2.NodeLocationID AND (ABS(NL.Latitude - NL2.Latitude) + ABS(NL.Longitude - NL2.Longitude)) / 2 <= 0.1
WHERE (NL.Latitude IS NOT NULL) AND (NL.Longitude IS NOT NULL)
AND (NL2.Latitude IS NOT NULL) AND (NL2.Longitude IS NOT NULL)
) AS D1
) AS D2
WHERE D2.Rnk=1