LATITUDE AND LONGITUDE

This exercise will show you how we describe locations on earth with geographical coordinates. You will also learn how to use Google Maps and Google Earth to visualize locations. You should go through the Google tutorial before answering the questions for this asignment. After you have gone through the information, you will be asked to answer some questions to check your skills.

The main points

Latitude and longitude are based on the equator and the prime meridian

Time zones show different local times but there is an international time, UTC

Map programs allow us to find latitude and longitude

The questions for this assignment

 

What are latitude and longitude?

The location of any place on the earth's surface can be described by its latitude and longitude. The lines that run east and west (left and right) are the latitude lines and the lines that run north and south (up and down) are the longitude lines. The lines are numbered as angles of a sphere measured from the center of the earth. The latitude measures the angle above or below the equator of a point at the surface.

The longitude measures the angle from the prime meridian, which runs through Greenwich, England.

The prime meridian was chosen so that the longitudes in Europe would increase eastward without duplication of values between east and west. The distance east or west of the prime meridian is measured by angles of 0 to 180 ° E or 0 to 180 ° W.

Each degree (symbol ° ) is divided into 60 minutes (symbol ' ) and each minute is divded into 60 seconds (symbol "). A given location would be described with degrees, minutes, and seconds of latitude and degrees, minutes, and seconds of longitude. For instance, a sample location might be 49°30'30" N latitude and, 123°30'30"W longitude. This the DMS system and is the most common system used.

Locations may also be specified as decimal fractions of degrees. This is called the decimal degree system DD. Thirty minutes is one half of a degree, so 45° 30' would be 45.5°

To convert the DMS 49° 30' 30" to decimal, you would start at the seconds. 30" / 60 = 1/2 minute. Add it to the minutes. 30' + .5 ' = 30.5' .Now change the minutes to degrees 30.5'/60 = .508 degree so 49° 30' 30"is 49.508 degrees.

Check yourself Try to answer these questions. You can check your answers by selecting the link below.

1. Suppose we have a location of 30° 30' 45" N latitude, 90° 50' 30" W longitude. Which letter is closest to that location on this globe?

2. What would be the decimal latitude and longitude?

check your answers here-

Maps are distorted.

Note in the globe diagram that the longitude lines get closer together as you go toward the poles. This means that a map that uses a even spaced grid causes distortion. This kind of map is called a Mercator projection and cannot show both the polar regions because of the distortion. Look at a map that shows Greenland and Australia. Actually, Australia is 3 times larger than Greenland but your map may make Greenland look larger.

All maps involve some distortion but the mercator maps make areas closer to the poles larger than they are.

 

 

Time Zones

The Earth is a sphere and since the Earth rotates every 24 hours, when the sun is overhead at noon, the opposite side of the earth is at midnight. Generally, every 15 degrees of longitude is also an hour different in time. Our local time (Central Standard Time) would be different anywhere more than 15 ° away from us. (Daylight savings time causes a shift of 1 hour when it is in effect but the time reference is based on standard time.)

If we want to refer to an event such as an earthquake, we want to refer to the time so people anywhere on the globe understand when it was. That international time zone is called Universal Coordinated Time or UTC. UTC uses a 24 hour clock so noon is 12 hours and 3 pm would be 12 + 3 or 15 hours.

UTC was formerly refered to as Greenwich Mean Time or GMT. The UTC is also based on the prime Meridian which runs through Greenwich England. England is at 0 degrees E or W and Chicago is near 90 degrees W so Chicago is one quarter the way around the earth.

That means we are one quarter of 24 hours or 6 hours different, The earth rotates conterclockwise as seen from the North pole so London has noon before we do in Chicago. That is if it is noon in London it is 6 AM standard time in Chicago. (During Daylight Savings Time we are only 5 hours earlier.) Chicago has a time designation of UTC - 6

Places to the East of the prime meridian have noon before London so their UTC designation is UTC + the hours difference.

180 degrees marks the point where one side of the longitude is just before midnight and the other side is after midnight and therefore the next day. This is called the International Date Line. (some adjustments are made for populated places so one place doesn't have two different days.)

Suppose an earthquake was reported to have occurred January 29, 2009 at 16:28 UTC. Chicago time is UTC -6:00 hours (standard). We would then know that the earthquake happened at 10:28 in the morning of January 29, 2009.

An excellent reference site for times zones is http://www.worldtimezone.com/time-us24.html

Check yourself 3 check your answers here

Suppose it is January 21, 2009 at 10:00 AM in Chicago. What time is it in London?

If Hawaii is UTC - 10 , what time is it in Hawaii?


Recently the US adopted a special grid, originally for military use throughout the world, called the Universal Transverse Mercator grid or UTM grid.

 

In this grid, the world is divided into 60 north-south zones, each covering a strip 6 wide in longitude. These zones are numbered consecutively beginning with Zone 1, which is between 180 and 174 west longitude, and progressing eastward to Zone 60, between 174 and 180 east longitude.

The zone number gives the location. From the diagram above you can see that Chicago is in zone 16.

 

The distance north or (South) from the equator is measured in meters and is called the Northing (or Southing). For instance, 16 359226E 4756749N is a location in zone 16 that is 4756749 meters North of the equator.

 

A line is given down the middle of each zone. A location in the zone is East of this line or West of this line. The center line is given a value of 500,000 meters. Distances to the west of this central meridian are less than 500,000 meters; to the east, more than 500,000 meters.

Our example location 16 359226E 4756749N is then in zone 16 and 359226 meters east (actually 140774 meters east of the centerline), and 4756749 meters north of the equator. This means it is in the west half of zone 16.

 

This system is pretty awkward for us but it is very easy for computers. Satellite navigation and GPS usually convert to degrees, minutes, and seconds. but they actually use the UTM.

Check yourself 4 : check your answers here

Chicago is in zone 16. Would Hawaii's zone number be greater or less than Chicago's?  

Using Internet Map Programs

There are a number of places here you can obtain maps online.

You can look up a location by latitude and longitude in Mapquest at http://www.mapquest.com/maps/latlong.adp

You can obtain maps from MSN and MSN virtual earth at http://maps.live.com/

Google maps are avilable at http://maps.google.com/

In this course we will concentrate on using Google maps and Google Earth

The Google Earth program can be downloaded and installed for free from earth.google.com/download-earth.html .

If you are working on a computer which is not your own, you may not be able to use Google Earth but you can generally use google maps on any computer.

There are a large number of sites on the internet that show how to use Google Earth. You can find many good videos on using Google Earth on You Tube.

A brief explanation of how to use the program for this course is given in this link. Google Earth Tutorial

There is also an online world atlas available at http://ngm.nationalgeographic.com/map/atlas/geophysical.html

There is also a very useful atlas and map maker available from http://www.nationalatlas.gov

Check your self 5. check your answers here

Use Google Earth and Google maps to answer these questions:

What is located at 36° 46' 56.20" N latitude and 103° 58' 16.27" W longitude?

What is the latitude & longitude of Meteor Crater in Arizona?

 

If you got these right, you should take a look at the questions for this exercise and find your answers before submitting them to Blackboard. See the questions