Geographic Location &
Time
Lab 1
Concepts
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The Earth’s Grid
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Latitude/parallels
Longitude/meridians
Prime Meridian, Equator
Great and small circles
Time and Time Zones

International Date Line
Grid System: Latitude & Longitude
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Latitude
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a.k.a “Parallels”
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
o
0 = Equator
Maximum extent
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Each line runs parallel to
all the others. They are
equally spaced apart
and never cross.
90oN at North Pole
90oS at South Pole
Lines run east to west
but measure distance
north and south
Grid System: Latitude & Longitude

Longitude
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a.k.a “Meridians”
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

o
0 = Prime Meridian
Maximum extent

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Lines converge at the
poles
o
180 … also called the
International Date Line
Lines run north to south
but measure distance
east and west
Grid System: Latitude & Longitude
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Degrees are subdivided into minutes and seconds.
The more detailed your location information is, the
more accurate it is.
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O
= degree symbol
’ = minute symbol
” = second symbol
1 degree = 60 minutes (1o = 60’)
1 minute = 60 seconds (1’ = 60”)
Note: minutes and seconds cannot exceed the
value of 60.

e.g., 75’ is incorrect. Should be written as 1o15’
Grid System: Latitude & Longitude

Always label your latitude and longitude!
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
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Latitude


Latitude labels = N or S
Longitude labels = W or E
Degrees range from 0o (at Equator) to 90o N or S. Cannot
exceed a value of 90.
Longitude

Degrees range from 0o (at Prime Meridian) to 180o
(International Date Line). Between those spots, a location
is either W or E of the Prime Meridian. Cannot exceed a
value of 180o.
Grid System: Latitude & Longitude
When identifying locations…
 Latitude comes before longitude
 Get as detailed as possible (at least
degrees and minutes).
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e.g., Atlanta’s location is: 33°45' N, 84°42′ W
Great Circles

A sphere divided exactly in
half by a plane which passes
right through its center.

The largest possible circle
you could manage to draw on
that sphere's surface

Despite the curved
appearance on flat maps,
great circle routes are the
shortest distance between
two points on Earth.
Small Circles

A circle produced by
planes passing through
a sphere anywhere
except through its
exact center.

Smaller than a great
circle (hence the clever
name).
Great or Small Circle?
You Decide
What are meridians?
What are parallels?
What is unique about the
Equator (relative to all
other parallels)?
Great Circle: example
The shortest path from Atlanta to Tokyo would fly
you through Canada, over Alaska, and down the
Pacific Rim. You would not pass straight across
the US and over the Pacific!
Tokyo,
Japan
Atlanta
Time
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Standard Time: legal time in an area
24 Standard Time Zones in the world
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Spaced 15o longitude apart, or 7.5o on each side of a Central
Meridian
GMT = Greenwich Mean Time



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“Zulu” time = military time (24 hr clock) based in Greenwich


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a.k.a. UTC = Coordinated Universal Time
The Prime Meridian runs directly through Greenwich, England
(just outside of London).
Time zones are typically referenced from GMT/UTC.
e.g., “1000Z” = 10am in Greenwich
e.g., “1500Z” = 3pm in Greenwich
EST = Eastern Standard Time
Central Meridians & Time Zones
Prime Meridian (0o)
EST is based on the 75oW meridian. There are 7.5o longitude on
either side of the meridian, making the time zone 15o longitude wide.
Time (con’t)

Time is 1 hour earlier when moving
East to West
Los Angeles
PST
5pm
W
Denver
MST
6pm
Chicago
CST
7pm
Note: EST is 5 hours “behind” (earlier) than GMT.
If it is 8pm EST, what time is it in Greenwich?
Atlanta
EST
8pm
E
International Date Line
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180o meridian (does not have a W or E label, just simply 180o)
When crossing W to E, it becomes the previous day
When crossing E to W, it becomes the next day
150oE
165oE
Tuesday Tuesday
4 am
5 am
West
180o
Tues. Mon.
6 am
165oW
150oW
Monday Monday
7 am
East
8 am