Reporting Geographic Coordinates
Geographic Coordinate Expressions
Degrees Minutes Seconds (DMS):
- Latitude: 40° 51' 59" N
- Longitude: 124° 4' 58" W
Decimal Degrees (DD):
- Latitude: 40.866389°
- Longitude: -124.082778°
Converting from DMS to Decimal Degrees
- 60 minutes = one degree
- 60 seconds = one minute
- 3600 seconds = one degree
DD = Degrees + (Minutes/60) + (Seconds/3600)
Latitude = 40 + (51/60) + (59/3600) N = 40.866389°
Longitude = 124 + (4/60) + (58/3600) W = -124.082778°
Degrees, Minutes, Seconds (DMS)
- Each degree contains 60 minutes
- Each minute contains 60 seconds
Coordinates for the same location can be expressed in different ways:
- 40° 31' 21" North by 105° 5' 39" West
- 40 31 21 N, 105 5 39 W
- 403121N, 1050539W
Decimal Degrees (DD)
We almost always need spatial data to be in Decimal Degrees in order to work with it in a computer.
| Name |
Longitude |
Latitude |
| Wagar 231, CSU |
-105.082° |
40.5750° |
| New Belgium |
-105.069° |
40.5930° |
| Paris |
2.2945° |
48.8582° |
| South Pole |
? |
-90° |
| Bird's Nest (China) |
116.391° |
39.9915° |
Spatial Accuracy in DMS
- The Earth is about 40,000 km around
- 40,000 / 360 degrees ~ 111 km/degree
- 111 km/degree / 60 minutes/degree ~ 1.85 km/minute
- 1.85 km/degree / 60 seconds/minute ~ 0.03 km/second (30 meters/second)
- To maintain 1 meter accuracy, we need to keep two digits after the seconds decimal!
Spatial Accuracy in DD
- The Earth is about 40,000 km around
- 40,000 / 360 degrees ~ 111 km/degree or 111,000 m/degree
- To maintain 1 meter accuracy, we need to keep 5 digits after the decimal!
Test Yourself
- Go to: http://geonames.usgs.gov/
- Search for a name
- What format are the coordinates in?
- What is the accuracy of the data?
Test Your Knowledge
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