Coordinate Converter
Why Are There Two Formats for Coordinates?
We live in a digital world, but our maps have a very old history. This clash between modern computers and ancient navigation gives us two conflicting ways to describe where we are.
When you look at a GPS unit, you are looking at the intersection of two imaginary lines that grid the Earth:
- Latitude: Horizontal lines (North/South). The Equator is 0°.
- Longitude: Vertical lines (East/West). Greenwich, England is 0°.
However, the way we write these numbers changes depending on if you are a computer or a sailor.
1. The Modern Format: Decimal Degrees (DD)
Computers, Google Maps, and your smartphone prefer this format. It expresses coordinates as a single float number.
Example: 40.7128, -74.0060 (New York City)
In this system, there are no N/S/E/W letters. Instead, direction is indicated by Positive and Negative symbols:
- Positive Latitude: North of Equator.
- Negative Latitude: South of Equator.
- Positive Longitude: East of Greenwich (Asia/Europe).
- Negative Longitude: West of Greenwich (Americas).
2. The Classic Format: Degrees, Minutes, Seconds (DMS)
This format dates back to ancient astronomers like Ptolemy. It divides the spherical earth into 360 degrees, just like a clock.
Example: 40° 42' 46" N, 74° 00' 21" W
Because a "Degree" covers about 69 miles (111 km), it isn't precise enough for navigation on its own. So, degrees are sliced into Minutes (') and Seconds (").
- 1 Degree = 60 Minutes.
- 1 Minute = 60 Seconds.
This system is sexagesimal (Base 60), which is incredibly annoying to calculate mentally but excellent for plotting on paper naval charts.
The "Missing Negative" Problem
The most common error when converting coordinates manually is forgetting the negative sign.
If you convert "74° West" to Decimal, the answer must be -74.0. If you forget the negative sign (74.0), you will end up in Kyrgyzstan (East) instead of New York (West)!
Accuracy: How Many Decimals Do You Need?
When looking at Decimal Degrees, how precise do you need to be? Each decimal place zooms you in closer.
| Decimal Place | Accuracy | Use Case |
|---|---|---|
| 1.0 | 111 km | Identify a large country or state. |
| 1.1 | 11 km | Identify a large city. |
| 1.11 | 1.1 km | Identify a village or neighborhood. |
| 1.1111 | 11 m | Identify a specific property/house. |
| 1.111111 | 11 cm | Professional surveying (Tectonics). |
Which One Should You Use?
Use Decimal Degrees (DD) if you are entering data into Google Maps, Python scripts, or Excel sheets. It is standard for digital data.
Use DMS if you are reading a paper map, using an older boat GPS, or reading legal land survey documents.