Selecting distinct combinations

Simply use the DISTINCT keyword:

SELECT DISTINCT Latitude, Longitude 
FROM Coordinates;

This will return values where the (Latitude, Longitude) combination is unique.

This example supposes that you do not need the other columns. If you do need them, i.e. the table has Latitude, Longitude, LocationName columns, you could either add LocationName to the distinct list, or use something along the lines of:

SELECT Latitude, Longitude, MIN(LocationName)
FROM Coordinates
GROUP BY Latitude, Longitude;