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Geographic Coordinates

Map of world showing the latitude and longitude , according to a projection type Eckert VI wide PDF (PDF, 1.8 MB). Latitude is marked along the vertical axis, but the longitude is not directly measurable by a horizontal measure, because this distance is reduced to the poles, to better match the actual distances on land, but could not give exact distances. Such a distortion of the distances (and angles and shapes) is inevitable with any projection on a flat map.

Geographic coordinates on a globe. The latitude is the degree of the angle marked phi (), the measurement of the angle marked lambda () relative to the reference meridian gives the longitude.

By geographic area (or "landmarks") of a place means the latitude , the longitude and sea level. To identify the surface of the planet, we can use another system called "benchmarks map.

To locate on the ground, it is necessary to use a datum which derive the geographical coordinates.

Summary

1 Latitude (Lat.)
Longitude 2 (length)
- 2.1 Articles Related
- 2.2 Links to external

/ / Latitude (Lat.)

Latitude is an angular value, expressing the position north - south from a point on Earth north or south of the equator.

Latitude is a measurement angle ranging from 0 to 90 at the equator to the poles.
This plane intersects the Earth's surface at an approximate circle (the circle of irregularities are related to changes in altitude), except at the poles where the circle is reduced to a point.
More latitude differs by 2, the further away from the plane of the equator, the latitude is however not a direct measure proportional to the distance between two planes, but proportional to the shortest distance to reach the equator in the earth's surface is traveling north or south geographic location. Indeed, the distance to the equatorial plane hardly changes near the poles even though the latitude varies greatly, unlike the plans of latitude near the equator where the variation of the interplane distance is maximum.

Longitude (length)

Longitude is an angular value, expressing the position is - west of a point on Earth.

All locations at the same longitude are a half-plane axis limited by the geographic poles, cutting the surface of the earth on a rough semicircle whose center is the center of the Earth, the arc going from one pole to another. Such a semi-circle is called the meridian.
Unlike the latitude (position north - south ) who benefits from the equator and poles as reference, there is no natural reference for longitude.
The longitude is a measure angle of 360 relative to a reference meridian, with a range from -180 to +180 or 180 respectively 180 west to east.
The reference meridian is the meridian of Greenwich (which also serves as a reference for time zones).

By combining the two angles, the position on the surface of the Earth can be specified.

For example, Baltimore (the U.S. ) has a latitude of 39.28 degrees north and longitude 76.60 degrees west ( 39 17 'N 76 36' W / 39.28, -76.6 ).

The geographical coordinates are traditionally expressed in the sexagesimal system (degrees () Minutes (') seconds (")). The basic unit is the degree angle (1 full turn = 360 ), then the minute of angle (1 = 60 '), then the second angle (1 '= 60 "). Measurements below the second are denoted with the decimal system.

Nowadays, the rating equivalent decimal minutes or decimal degrees are also used:

DMS Degree: Minute: Second (49 30 '00 "- 123 30' 00")
MD Degree: Minute (49 30.0 '- 123 30.0')
DD Decimal Degree (49.5000 - 123.5000 ), generally with 4 decimal places.

The WGS 84 is the datum associated with the system GPS and it has quickly become the universal reference for mapping.

Caution: do not confuse the angular measurements of longitude used in geography, with hourly measurements, especially for units minutes and seconds, because if we admit that the day length is 24 hours (the exhibition solar zenith performs the full rotation of the Earth, that is to say 360 , 24 h), then for the mean solar day:

Longitude 15 correspond to a difference of one hour (60 minutes long)
So 1 longitude corresponds to a gap of 4 min schedules,
15 'longitude correspond to 1 min time
15 "longitude corresponds to 1 s schedule.

These historical equivalences are approximate, but are more accurate now because the definition and measurement of time (in seconds SI) is no longer based on the duration of diurnal rotation land whose duration varies not only with places and seasons, but also from one year to another, the rotation of the Earth is not uniform and tend to slow down (so the duration of solar day tend to lengthen over time, also with periods less Frequently when this duration decreases, more solar day is exactly 24 hours during each 60-min time during the last 60 seconds of time).

For these reasons, we should not use the symbols of SI units of time (that is to say, min for minute and s for second) to record the angular measurements such as longitude and latitude, because of ambiguities that armature.