I have a table that I use to retrieve drive times, according to longitude and latitude of the origin and destination. Although I am using Google's API to find new commute times, I store the results of previous queries locally so that if I need to query the same drive again, I won't have to use Google. (Google's web service is throttled.) Anyway, the table includes five columns:
LatStart (smallmoney)
LongStart (smallmoney)
LatEnd (smallmoney)
LongEnd (smallmoney)
DriveTime (Int. In seconds)
(Smallmoney, it turns out, works very well for longitude and latitude, as long as you only need four digits after the decimal, which is precise enough for this.)
My question is: For optimal performance in SELECT queries, should I index all four longitude / Latitude columns?
And a second question: We can assume that it won't delete very often, but in the long run as the table grows, it will still insert rows about 25% as often as it selects rows. Therefore, will an index on all four columns be detrimental to insert queries?