Your geographic coordinates are (probably) too precise

You don’t need six digits of precision to find your car

When I ran a commercial geocoding service I took lists of addresses and returned the latitude and longitude of the addresses. This was in the halcyon days of creative energy after the first dot-com bust.

And people often, OFTEN! Complained about the precision of my returned data.

They wanted more decimal points of precision. And it was in fact, absurd!

But how many decimals of precision do you need?

At the equator one degree of longitude is 60 nautical miles, and that is true everywhere for latitude. Degrees are divided into 60 minutes. Leading to the sailor’s adage: “A minute’s a mile the world around.”

A nautical mile is about 1.15 statute miles. So a degree is 69.17 statute miles.

Given that, a minute of latitude, or of longitude at the equator, is 6.9 miles.

Decimal Places | Notation | Distance | Real-World Scale — — — — — — — -| — — — — — — — | — — — — — — — — — -| — — — — 0 | 1° | 69.17 miles | City-to-city 1 | 0.1° | 6.92 miles | Town / county 2 | 0.01° | 3,652.2 feet | Neighborhood 3 | 0.001° | 365.2 feet | City block 4 | 0.0001° | 36.5 feet | Backyard 5 | 0.00001° | 3.7 feet | Parked car 6 | 0.000001° | 4.383 inches | Where is my pillow? 7 | 0.0000001° | 0.438 inches | Precision instrument 8 | 0.00000001° | 43.83 thou (mil) | You are using a mill or a lathe with a micrometer

In metric:

Decimal Places | Notation | Distance | Real-World Scale — — — — — — — -| — — — — — — — -| — — — — — — — — — -| — — — 0 | 1° | 69.17 miles | City-to-city 1 | 0.1° | 6.92 miles | Town / county 2 | 0.01° | 3,652.2 feet | Neighborhood 3 | 0.001° | 365.2 feet | City block 4 | 0.0001° | 36.5 feet | Backyard 5 | 0.00001° | 3.7 feet | Parked car 6 | 0.000001° | 4.383 inches | Where is my pillow? 7 | 0.0000001° | 0.438 inches | Precision instrument 8 | 0.00000001° | 43.83 thou (mil) | You are using a mill or a lathe with a micrometer

You can convert a longitude distance by multiplying that value by the cosine of the latitude. If you are tying to get distances where the latitude and longitude change you need another tool, like the Haversine formula.

But that is beyond the scope of this article.

Here are prettier images of the tables.