Explanatory Items > 4

4 Coordinates

The coordinates of plot and subplot centres or reference points are specified in:

Degrees Minutes Seconds (D° M’ S“) with a leading “+” or “-”

GENERAL REMARKS

Datum

All coordinates used in the ICP Forests database are based on the datum WGS84 (World Geodetic System 1984).

Latitude

Examples in the format used by the ICP Forests database:

  • 50 degree, 20 minutes, 27 seconds North corresponds to +502027
  • 9 degree, 5 minutes, 7 seconds North corresponds to +090507

Location:

  • north-south position
  • positive values = Northern Hemisphere (North of the equator)
  • negative values = Southern Hemisphere (South of the equator)

Distance:

  • 1 degree ~ 111.1 km
  • 1 minute ~ 1.852km
  • 1 second ~ 30.5m

Longitude

Examples in the format used by the ICP Forests database:

  • 2 degree, 37 minutes, 9 seconds West corresponds to -023709
  • 17 degree, 40 minutes, 45 seconds East corresponds to +174045

Location:

  • east-west position
  • positive values = East of the prime meridian in Greenwich
  • negative values = West of the prime meridian in Greenwich

Distance:

  • 1 degree ~ 111.1 x cos(latitude) km
  • 1 minute ~ (111.1 x cos(latitude)) / 60 km
  • 1 second ~ (111.1 x cos(latitude)) / 3.6 m

The parallel circles of latitude become smaller towards the poles, so the length of a degree of longitude depends on the latitude.

Examples of different distances of longitude in km or m throughout the area of the ICP Forests network:

location Latitude (N) 1 degree of longitude 1 minute of longitude 1 second of longitude
Madrid 40° 85km 1.42km 23.6m
Warsaw 52° 68km 1.14km 18.9m
North Norway 70° 38km 0.63km 10.5m

E.g. In Madrid 1° of longitude corresponds to 85km whereas in North Norway it corresponds to 38km

REPRESENTATIONS

The same geographic coordinates can be represented in different formats:

  • Degree Minutes Seconds (D° M’ S“) - Used in the ICP Forests database

  • Decimal Degrees (D.D°) - Representation as a single number sequence

  • Decimal Minutes (D° M.M’) - Default in many GPS units

CONVERSIONS

Degrees Minutes Seconds (D° M’ S“) TO Decimal Degrees (D.D°)

D.D° = d + (m/60) + (s/3600)

EXAMPLE:

D° M' S" = 30d 14m 4s

D.D° = 30 + (14/60) + (4/3600) = 30.2344444°

Degrees Minutes Seconds (D° M’ S“) TO Decimal Minutes (D° M.M’)

D° M.M’ = d AND m + (s/60)

EXAMPLE:

D° M' S" = 30d 14m 4s

D° M.M' = 30 AND 14 + (4/60) = 30° 14.066666'

Decimal Degrees (D.D°) TO Degrees Minutes Seconds (D° M’ S“)

d = integer(D.D°)

m = integer((D.D° - d) × 60)

s = integer((D.D° - d - m/60) × 3600)

EXAMPLE:

D.D° = 30.2345555

d = integer(30.2345555) = 30°

m = integer((30.2345555 - 30) × 60) = 14'

s = integer((30.2345555 - 30 - 14/60) × 3600) = 4''

ICP Forests format: "+301404"

Note - This conversion inculdes a loss of precision!

Decimal Minutes (D° M.M’) TO Degrees Minutes Seconds (D° M’ S“)

d = D° FROM D° M.M’

m = integer(M.M’)

s = round(M.M’ - integer(M.M’)) x 60

EXAMPLE:

D° M.M' = 30° 14.066666'

d = 30

m = integer(14.066666) = 14

s = round(14.066666 - integer(14.066666)) x 60 = 4

Abbreviations:

d = degrees

m = minutes

s = seconds

D.D° = Decimal Degrees

D° M' S" = Degrees Minutes Seconds

D° M.M' = Decimal Minutes