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LOCATIONAL SETTINGS
A location is the place where a particular point or object
exists. Location is an important term in geograph! an" isusuall consi"ere" more precise than #place.# A localit is a
human settlement$ cit! town! %illage! or e%en archaeological
site.
Locational settings $
A location in the earth can be locate" b latitu"es &
longitu"es. This locational setting is "one b Geographiccoor"inate sstem. A geographic coor"inate sstem is
a coor"inate sstem that enables e%er location on the Earth to
be speci'e" b a set o( numbers or letters. The coor"inates are
o(ten chosen such that one o( the numbers represents %ertical
position! an" two or three o( the numbers represent hori)ontal
position. A common choice o( coor"inates
is latitu"e! longitu"e an" ele%ation.
A geographic coordinate system (GCS) uses a three-dimensional
spherical surface to define locations on the earth. A GCS is often incorrectly
called a datum, but a datum is only one part of a GCS. A GCS includes an
angular unit of measure, a prime meridian, and a datum (based on a spheroid).
A point is referenced by its longitude and latitude values. Longitude and
latitude are angles measured from the earths center to a point on the earths
surface. !he angles often are measured in degrees (or in grads). !he follo"ing
illustration sho"s the "orld as a globe "ith longitude and latitude values.
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#n the spherical system, hori$ontal lines, or east%"est lines, are lines ofe&ual latitude, or parallels. 'ertical lines, or north%south lines, are lines of e&ual
longitude, or meridians. !hese lines encompass the globe and form a gridded
net"or called a graticule.
!he line of latitude mid"ay bet"een the poles is called the e&uator. #t
defines the line of $ero latitude. !he line of $ero longitude is called the prime
meridian. or most geographic coordinate systems, the prime meridian is the
longitude that passes through Green"ich, *ngland. +ther countries use
longitude lines that pass through ern, ogota, and aris as prime meridians.
!he origin of the graticule (,) is defined by "here the e&uator and prime
meridian intersect. !he globe is then divided into four geographical &uadrants
that are based on compass bearings from the origin. /orth and south are above
and belo" the e&uator, and "est and east are to the left and right of the prime
meridian.
!his illustration sho"s the parallels and meridians that form a graticule.
Latitude and longitude values are traditionally measured either in decimal
degrees or in degrees, minutes, and seconds (01S). Latitude values are
measured relative to the e&uator and range from -23 at the South ole to 423
at the /orth ole. Longitude values are measured relative to the prime meridian.
!hey range from -563 "hen traveling "est to 563 "hen traveling east. #f the prime meridian is at Green"ich, then Australia, "hich is south of the e&uator
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and east of Green"ich, has positive longitude values and negative latitude
values.
#t may be helpful to e&uate longitude values "ith 7 and latitude values
"ith 8. 0ata defined on a geographic coordinate system is displayed as if a
degree is a linear unit of measure. !his method is basically the same as the lateCarr9e pro:ection.
Although longitude and latitude can locate e;act positions on the surface
of the globe, they are not uniform units of measure. +nly along the e&uator does
the distance represented by one degree of longitude appro;imate the distance
represented by one degree of latitude. !his is because the e&uator is the only
parallel as large as a meridian. (Circles "ith the same radius as the spherical
earth are called great circles. !he e&uator and all meridians are great circles.)
Above and belo" the e&uator, the circles defining the parallels of latitudeget gradually smaller until they become a single point at the /orth and South
oles "here the meridians converge. As the meridians converge to"ard the
poles, the distance represented by one degree of longitude decreases to $ero. +n
the Clare 56<< spheroid, one degree of longitude at the e&uator e&uals 555.=>5
m, "hile at <3 latitude it is only ??.6> m. ecause degrees of latitude and
longitude dont have a standard length, you can@t measure distances or areas
accurately or display the data easily on a flat map or computer screen.
Tpes o( Location $
Absolute Location
Absolute location "escribes the location o( a place base"
on a 'xe" point on earth. The most common wa is to i"enti(
the location using coor"inates such aslatitu"e an" longitu"e.
Lines o( longitu"e an" latitu"e crisscross the earth.
Latitude is used to mar the north-south position of a location on the *arth@ssurface and ranges from degrees at the e&uator to 2 degrees at the /orth and
South oles. !here are 56 degrees of latitude and the distance bet"een each
degree of latitude is roughly <2 miles (555 m).
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An e;ample of an absolute location using latitude and longitude is
the nited States Capitol "hich is located at =63 ?=B =? /, DD3 B => E.
Latitude is al"ays "ritten first and latitude and longitude are composed of
degrees, minutes, and seconds (01S).
Absolute location can also refer to an address, the street address of the S
State Capitol is irst St S* in Eashington, 0C >F. #n both instances,absolute location refers to a fi;ed point based on an abstract net"or of
imaginary locations.
Relative Location
elative location refers to the position of a place or entity based on its
positive "ith respect to other locations. or e;ample, the location of the S
Capitol is located about =6 miles south"est of altimore. elative location can
be e;pressed in terms of distance, travel time, or cost.
elative location can also be used to provide geographic conte;t. or
e;ample, overvie" or locator maps sho" the relative location of a place or
entity based on a larger geographic vie". or e;ample, the inset map belo",
sho"s the relative location of the state of !e;as "ithin the nited States.
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