By David Okul
Nov 30, 2020
Coordinate systems are measurements used to describe a position on the earth surface. They depend on the way the data is stored in mapping. For instance,
Map units are in decimal degrees (degrees, minutes, and seconds expressed as a decimal) if data is stored in geographical coordinate system. Conversely, data stored in projected coordinate have mapping units in meters or feet. Map units can be altered by changing the data’s coordinate system.
Coordinate systems are often expressed as 2-dimensional, but we live in a 3-dimensional earth. The components of a coordinate reference system determine how flattening of the data exist in 3-D space. There are different ways of reporting coordinates, some of which include
- Universal Transverse Mercator (UTM)
- Decimal degrees
- Degrees Minutes Seconds (DMS)
- Degrees Decimal Minutes (DDM)
Use of any system will depend on the purpose of the location and personal preferences.
Universal Transverse Mercator (UTM)
Written Format
- UTM zone 37M, 316195E, 9662938N
Other reports will require you to include ‘m’ for meters while writing coordinates in UTM. As such the zone would be UTM zone 37M, 316195mE, 9662938mN
The position is of Mount Kilimanjaro in Tanzania.
The Eastings are meters on the x-axis (6 numbers), and northings are meters on the y-axis (7 numbers). Significant part of East Africa is in the UTM zone 37M. You can check the various UTM zones here.
Many organizations prefer to use UTM while doing fieldwork because it is easier to write (i.e., no need of degrees, minutes, negative signs, or compass directions.
Decimal Degrees (DD)
Written format:
- 04820°S, 37.34610°W; or -3.04820, 37.34610
The location is still of Mounty Kilimanjaro, in Tanzania, East Africa.
DD should have 5 or more decimal places to be accurate.
Decimal degrees are among the most commonly used coordinate reference systems. For instance, mapping applications such as Google Maps primarily use it.
Degrees Minutes Seconds (DMS)
Written format:
- 3° 2′ 53.5″S, 37° 20′ 46.0″E; or -3° 2′ 53.5″, 37° 20′ 46″
It is the oldest way of reporting geographic coordinates
The negative sign indicates the direction of the meridian.
Longitude is the x-axis and latitude is the y-axis. For this reason, some write longitude before latitude (software programs).
Degrees Decimal Minutes (DDM)
Written format:
-3° 2.892′, 37° 20.766′; or 3° 2.892 S, 37° 20.766 E
The location is still Mount Kilimanjaro
DDM should have 2 or more decimal places to be accurate.
Apart from the coordinate systems, some reports will require information about the datum.
David Okul is an environmental management professional with over 10 years experience on donor projects, forestry, and community-based natural resources management.
