Have function to compare and select numbers base on range using SqlCe for Windows phone

Hi, I store all the GPS Location in SqlCe DB for all the streets I had been there before.  The purpose of this Windows Phone app is to quickly check all the GPS location in the Database and find a match or number in the range.  Say, I store these LatLon in the table, for example : 

tableGps

longLat 

longLon

Lat          Lon

-----         -----------

Rockefeller center
40.75883,       -73.979831

40.759594,     -73.978565
40.757985,     -73.978758
40.760017,     -73.98174

Question :

1) How do I make comparison or matching  that I am around within the range .

Say my current GPS location is  :40.75783,       -73.979631  which is closer to Rockefeller center. 

2) How to spcifiy the range that is acceptable. say within 3% ?

Your help is much appreciated.

Thanks