Latitude, usually denoted symbolically by the Greek letter φ, gives the location of a place on Earth north or south of the Equator. Latitude is an angular measurement ranging from 0° at the Equator to 90° at the poles (90° N or 90° S). Co-latitude is the complement of latitude.

Lines of latitude

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All locations of a given latitude are collectively referred to as a line of latitude or parallel, because they are coplanar, and all such planes are parallel to the Equator. Lines of latitude other than the Equator are approximately small circles on the surface of the Earth; they are not geodesics since the shortest route between two points at the same latitude involves moving farther away from, then towards, the equator. A specific latitude may then be combined with a specific longitude to give a precise position on the Earth's surface. Certain lines of latitude are important such as the Arctic Circle, Tropic of Cancer, Tropic of Capricorn or Antarctic circle.

Subdivisions

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Each degree of latitude is further sub-divided into 60 minutes (one minute of latitude is very close to one nautical mile or 1852 metres although this itself varies slightly with latitude (at sea level) because the earth is shaped like a slightly oblate orange), each of which divides into 60 seconds. A latitude is thus specified as 13°19′43″ N. For high accuracy, the seconds are specified with a decimal fraction. An alternative representation uses degrees and minutes, where parts of a minute are expressed as a decimal fraction, thus: 13°19.717′ N. Degrees expressed as a decimal number (decimal degree notation) is more often used: 13.32861° N. Sometimes, the north/south suffix is replaced by a negative sign for south (−90° for the South Pole).

Important latitudes

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Latitudes of particular importance are the Tropic of Cancer (latitude 23°27′ north), the Tropic of Capricorn (latitude 23°27′ south), the Arctic Circle (latitude 66°33′ north), and the Antarctic Circle (latitude 66°33′ south). Only at latitudes between the Tropics is it possible for the sun to be at the zenith. Only north of the Arctic Circle or south of the Antarctic Circle is the midnight sun possible.

Effect of latitude

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A region's latitude has a great effect on its climate and weather (see Effect of sun angle on climate). Latitude more loosely determines tendencies in polar auroras, prevailing winds, and other physical characteristics of geographic locations.

Types of latitude

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Because the Earth is slightly flattened by its rotation, cartographers refer to a variety of auxiliary latitudes to precisely adapt spherical projections according to their purpose.

Common "latitude"

• In common usage, "latitude" refers to geodetic or geographic latitude φ and is the angle between the equatorial plane and a line that is normal to the reference spheroid, which approximates the shape of the Earth to account for flattening of the poles and bulging of the equator.

The expressions following assume elliptical polar sections with eccentricity e, and that all sections parallel to the equatorial plane are circular. Geographic latitude (with longitude) then provides a Gauss map.

Reduced latitude

• Reduced or parametric latitude β is the latitude of the same radius on the sphere with the same equator.

$\backslash beta=\backslash arctan\; \backslash left(\; \backslash sqrt\{1-e^2\}\; \backslash cdot\; \backslash tan\; \backslash phi\; \backslash right)$

Authalic latitude

• Authalic latitude ξ gives an area-preserving transform to the sphere.

$\backslash xi=\backslash arcsin\; \backslash left\backslash frac\{Q\; \backslash left(\; \backslash phi\; \backslash right)\}\{Q\; \backslash left(\; \backslash frac\{\backslash pi\}\{2\}\; \backslash right)\}\; \backslash right,\; \backslash quad\; \backslash mathrm\{where\}\; \backslash \; Q\; \backslash left(\backslash phi\backslash right)\; =\; \backslash left|\backslash frac\{\backslash sin\; \backslash phi\}\{1\; -\; (e\; \backslash cdot\; \backslash sin\; \backslash phi)^2\}\; -\; \backslash frac\{1\}\{2e\}\; \backslash cdot\; \backslash ln\; \backslash left(\; \backslash frac\{1\; -\; e\; \backslash cdot\; \backslash sin\; \backslash phi\}\{1\; +\; e\; \backslash cdot\; \backslash sin\; \backslash phi\}\; \backslash right)\; \backslash right|$

Rectifying latitude

• Rectifying latitude μ is the surface distance from the equator, scaled so the pole is 90°. Unfortunately, it is an incomplete elliptic integral:

$\backslash mu\; =\; k\; \backslash int\_\{x=0\}^\backslash phi\; \backslash frac\{1\}\{\backslash left1\; -\; (e\; \backslash cdot\; \backslash sin\; x)^2\; \backslash right^\backslash frac\{3\}\{2\}\}\; \backslash \; dx$

Conformal latitude

• Conformal latitude χ gives an angle-preserving (conformal) transform to the sphere.

$\backslash chi\; =\; 2\; \backslash cdot\; \backslash arctan\; \backslash sqrt\{\backslash frac\{1\; +\; \backslash sin\; \backslash phi\}\{1\; -\; \backslash sin\; \backslash phi\}\; \backslash cdot\; \backslash left(\; \backslash frac\{1\; -\; e\; \backslash cdot\; \backslash sin\; \backslash phi\}\{1\; +\; e\; \backslash cdot\; \backslash sin\; \backslash phi\}\; \backslash right)^e\}\; -\; \backslash frac\{\backslash pi\}\{2\}$

Geocentric latitude

• The geocentric latitude φ_g is the angle between the equatorial plane and a line from the center of the Earth.

$\backslash phi\_g\; =\; \backslash arctan\; \backslash left(1\; -\; e^2)\; \backslash cdot\; \backslash tan\; \backslash phi\; \backslash right$

For other planets such as Mars, geographic and geocentric latitude are called "planetographic" and "planetocentric" latitude, respectively. Most maps of Mars since 2002 use planetocentric coordinates.

Approximate difference from geographic latitude
φ	reduced φ − β	authalic φ − ξ	rectifying φ − μ	conformal φ − χ	geocentric φ − φg
0°	0.00′	0.00′	0.00′	0.00′	0.00′
5°	1.01′	1.35′	1.52′	2.02′	2.02′
10°	1.99′	2.66′	2.99′	3.98′	3.98′
15°	2.91′	3.89′	4.37′	5.82′	5.82′
20°	3.75′	5.00′	5.62′	7.48′	7.48′
25°	4.47′	5.96′	6.70′	8.92′	8.92′
30°	5.05′	6.73′	7.57′	10.09′	10.09′
35°	5.48′	7.31′	8.22′	10.95′	10.96′
40°	5.75′	7.66′	8.62′	11.48′	11.49′
45°	5.84′	7.78′	8.76′	11.67′	11.67′
50°	5.75′	7.67′	8.63′	11.50′	11.50′
55°	5.49′	7.32′	8.23′	10.97′	10.98′
60°	5.06′	6.75′	7.59′	10.12′	10.13′
65°	4.48′	5.97′	6.72′	8.95′	8.96′
70°	3.76′	5.01′	5.64′	7.52′	7.52′
75°	2.92′	3.90′	4.39′	5.85′	5.85′
80°	2.00′	2.67′	3.00′	4.00′	4.01′
85°	1.02′	1.35′	1.52′	2.03′	2.03′
90°	0.00′	0.00′	0.00′	0.00′	0.00′

Astronomical latitude

• A more obscure measure of latitude is the astronomical latitude, which is the angle between the equatorial plane and the normal to the geoid (ie a plumb line). It originated as the angle between horizon and pole star.

Latitude and wealth

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It is frequently observed that there is a distinct correlation between latitude and the wealth of nations. The continents along the equator, Africa and South America are the poorest. Even within Africa and South America this can be seen as the nations furthest from the equator are wealthier. In Africa the wealthiest nations are the three on the southern tip of the continent, South Africa, Botswana, and Namibia, and the countries of North Africa. Similarly in Latin America Argentina, Chile and Uruguay have long been the wealthiest. Within Asia, Indonesia, located on the equator, is among the poorest. The wealthiest nations of the world with the highest standard of living tend to be those at the northern extreme of areas open to human habitation, Canada, and the Nordic Countries. Within the wealthy continents, and even within large countries wealth increases with distance from the equator. Southern Europe has long been poorer as has the Southern United States.

There have been a number of explanations for this phenomenon. The first to describe and try to assess it was the French philosophe Montesquieu who proposed that cold weather means less blood in the extremities, which makes the flesh less elastic; this gives northerners more strength and makes them less able to relax. This forcing of the blood inward, according to Montesquieu also means more flows through the heart, increasing vitality. These findings have been wholly discredited by modern science.

There are also exceptions, for example, Russia is less well off than Unitied States, or even Australia, the latter country is wealthier than Southern Europe. Also, within Russia, Moscow and especially St. Petersburg are wealthier than, for example, Siberia. Germany's poorest regions are situated in the North East.

Evolutionary explanations

One explanation currently being promoted by supporters of eugenics, is claimed to be grounded in evolutionary theory. Some have argued that as humans migrated into higher latitudes and encountered colder weather there, the cold weather forced the evolution of higher group intelligence by forcing inhabitants to perform more intellectually demanding tasks, such as building shelter, fires, and clothing, in order to survive (Lynn, 1991).

One study that supports this notion was performed by Beals et al. (1984, p. 309), who found a correlation of 0.62 (p=0.00001) between latitude and cranial capacity in samples worldwide and reported that each degree of latitude was associated with an increase of 2.5 cm³ in cranial volume.

Researchers such as psychologist J. Philippe Rushton have argued that the association of greater brain size with greater latitude is due to the fact that cold weather imposes on its inhabitants more cognitively demanding tasks such as the need to construct shelter, make clothing, and store food.

Nevertheless, these explanations seem to be contradicted by the fact that it was in Africa, at near equatorial latitude, that harsh conditions such as extreme drought have brought our species, homo sapiens, to existence. Another contradicting observation is the high number of advanced civilizations that flourished near the equator -- such as Sumerian, Egyptian, Hindu among many others. The demanding tasks of shelter construction, cloth making and food storing, seem to be less likely to have constrained man's evolution since the invention of agriculture and writing.

Non-evolutionary explanations

Another explanation that is still widely held is that modern technologies and institutions were designed primarily in a small area of north western Europe. Thus agricultural techniques, machines, and medicines were designed to suit a temperate climate. These technologies and models readily spread to areas of similar climate, such as North America and Australia. As these areas also became centres of innovation this bias was further enhanced. Vastly less effort has been put into improving tropical agriculture than temperate because of this. Technologies, from automobiles to power lines are designed for colder drier regions and tend to work far worse in the tropics.

Thus, there exists a feedback effect of technologies being designed for the wealthy, which makes them more wealthy and thus more able to fund technological development. One piece of evidence for this is that the far north has not always been the wealthiest latitude. Until only a few centuries ago, the wealthiest belt stretched from Southern Europe through the Middle East, northern India and southern China. A dramatic shift in technologies beginning with ocean going ships and culminating in the Industrial Revolution saw the most developed belt move north, in Europe, in China, and in the Americas. Northern Russia became a superpower while southern India became impoverished and colonized. Such dramatic changes argue that the current distribution of wealth is not due to immutable factors such as climate or race. Evidence of this is that the agricultural revolution occurred first in ancient Mesopotamia.

Linked to this explanation is that of disease. The tropics are far more prone to devastating diseases due to their temperature that makes life easier on vectors such as insects and rodents. There has long been a malarial belt spanning the globe; this made human life more difficult. Most notably it was almost impossible for most forms of northern livestock to thrive. The disparities have been compounded by the wealth of the north: vastly more research money goes into curing the ailments of northerners.

Physiologist Jared Diamond, in his Pulitzer Prize-winning work Guns, Germs, and Steel, made the case that the Europe-Asia land mass is particularly favorable for the transition of societies from hunter-gatherer to farming communities. The continent stretches much further along the same lines of latitude than any of the other continents. As it is much easier to transfer a domesticated species along the same latitude than it is to move it to a warmer or colder climate, any species developed at a particular latitude will be transferred across the continent in a relatively short amount of time. Thus the inhabitants of this continent have a built-in advantage in terms of earlier development of farming, and a greater range of plants and animals from which to choose.

He also linked this progression to the development of diseases that were later to threaten the inhabitants of other continents. The close association of people in Europe-Asia with their domesticated animals provided a vector for the rapid transmission of diseases. Inhabitants of lands with few domesticated species were never exposed to the same range of diseases, and so, at least on the American continents, succumbed to diseases introduced from Europe.

Further reading

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• John P. Snyder Map Projections: a working manual USGS

See also

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• Geographic coordinate system
• Geodetic system
• Geodesy
• Great-circle distance
• Horse latitudes
• List of cities by latitude
• List of cities by longitude
• Longitude
• Navigation

References

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External links

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• Free GeoCoder
• GEONets Names Server, access to the National Geospatial-Intelligence Agency's (NGA) database of foreign geographic feature names.
• Look-up Latitude and Longitude
• Resources for determining your latitude and longitude
• Convert decimal degrees into degrees, minutes, seconds - Info about decimal to sexagesimal conversion
• Latitude and longitude converter – Convert latitude and longitude from degree, decimal form to degree, minutes, seconds form and vice versa. Also included a farthest point and a distance calculator.
• NASS - Convert degrees/minutes/seconds to decimal degrees and vice versa - JavaScript version
• Worldwide Index - Tageo.com – contains 2,700,000 coordinates of places including US towns
  • for each city it gives the satellite map location, country, province, coordinates (dd,dms), variant names and nearby places.
• Distance calculation based on latitude and longitude - JavaScript version
• Zoomable version of the map

Lines of latitude | Navigation | Angle

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