How do we measure coordinates?
We measure geographical coordinates, primarily longitude and latitude, using angular units based on the Earth's sphere.
Geographical coordinates provide a system for locating points on the Earth's surface. This system uses two main measurements: latitude and longitude.
Latitude
Latitude measures the angular distance, in degrees, of a point north or south of the Earth's equator.
- Equator: The starting point for latitude, designated as 0 degrees.
- North Pole: 90 degrees North (90° N).
- South Pole: 90 degrees South (90° S).
- The range for latitude is 180° (90° N ↔ 90° S).
Longitude
Longitude measures the angular distance, in degrees, of a point east or west of the Prime Meridian (also known as the Greenwich Meridian).
- Prime Meridian: The starting point for longitude, designated as 0 degrees.
- International Date Line: Roughly follows the 180-degree meridian.
- Longitude ranges from 0° to 180° East (E) and 0° to 180° West (W).
- The total range for longitude around the Earth is 360°.
The Units of Measurement: Degrees, Minutes, and Seconds
The primary unit in which longitude and latitude are given is degrees (°). As stated in the reference:
- There are 360° of longitude (180° E ↔ 180° W).
- There are 180° of latitude (90° N ↔ 90° S).
For more precise location measurements, each degree can be broken down into smaller units:
- Each degree can be broken into 60 minutes (').
- Each minute can be divided into 60 seconds (”).
This system is often referred to as Degrees, Minutes, and Seconds (DMS).
Coordinate Formats
Coordinates can be expressed in different formats:
- Degrees, Minutes, Seconds (DMS): E.g., 40° 45' 0" N, 74° 0' 0" W (Near New York City)
- Decimal Degrees (DD): E.g., 40.75°, -74.00° (Equivalent to the above)
Using DMS allows for very specific locations to be identified. For instance:
- 1 degree of latitude is approximately 69 miles (111 kilometers).
- 1 minute of latitude is approximately 1.15 miles (1.85 kilometers).
- 1 second of latitude is approximately 0.02 miles (31 meters).
Longitude distances vary depending on latitude, being widest at the equator and converging at the poles.
Example Coordinate Measurement
To measure a coordinate, imagine a line drawn from the center of the Earth to the specific point on the surface.
- The latitude is the angle between this line and the equatorial plane.
- The longitude is the angle between the plane containing this line and the Earth's axis (meridian plane) and the plane of the Prime Meridian.
Specialized instruments like GPS (Global Positioning System) receivers use signals from satellites to calculate these angles and determine the precise latitude and longitude of a location on the Earth's surface.
