IV-w4 lat & long
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Using Latitude and Longitude - Lesson 1

How can I remember which lines are which?

head spinning

Latitude lines are imaginary lines on the earth's surface. They run east and west around the globe and tell you your distance north or south of the Equator.

Think of latitude like the rungs of a ladder (ladder sounds a lot like latitude). Latitude lines run east and west, but they tell how far up (north) you can go or how far down (south) you can go.

ladderlatitude

 

Longitude lines are imaginary lines on the earth's surface that run from pole to pole around the globe and tell you your distance east or west from the Prime Meridian.

When you think of longitude, think of long, tall telephone poles (because longitude lines run from pole to pole). Longitude lines run north and south, but they tell how far east you can go or how far west you can go.

pole line  longitude

 

Using Latitude and Longitude - Lesson 2

Why are latitude and longitude measured in degrees?

In the field of mathematics, circles are measured in degrees. There are 360 degrees in a circle. Since the earth is basically circular, it was decided to measure latitude and longitude in degrees also.

The first latitude line was the Equator (equally distant between the north and south poles). It is the largest of all latitude lines. All other latitude lines are measured in degrees north or south of the Equator. There are a maximum of 90 degrees of latitude to the north or the south of the Equator.

latitude


The first longitude line was the Prime Meridian. Any meridian could have been chosen as the Prime Meridian because they are all exactly the same. The Prime Meridian was selected by international agreement at the International Meridian Conference called by President Chester Arthur in October of 1884. Representatives from 25 nations met in Washington, D.C. All other longitude lines are measured in degrees east or west of the Prime Meridian. There are a maximum of 180 degrees on longitude to the east or the west of the Prime Meridian.

longitude


It is approximately 70 miles between two latitude lines. For more accuracy in location, degrees can be divided into smaller parts. One degree can be divided into 60 minutes (') and one minute can be divided into 60 seconds (").

Thanks to Mr. Brad Bowerman, Social Studies Teacher  at Lakeland High School, Jermyn, PA
for the use of his copyrighted text.

http://www.lakelandsd.com/tutorial/

Symbols for degrees, minutes and seconds:

°

Degrees

'

Minutes

"

Seconds

The three common formats:

DDD° MM' SS.S"

Degrees, Minutes and Seconds

DDD° MM.MMM'

Degrees and Decimal Minutes

DDD.DDDDD°

Decimal Degrees

Degrees, Minutes and Seconds

DDD° MM' SS.S"
32° 18' 23.1" N 122° 36' 52.5" W

This is the most common format used to mark maps. It's also the most cumbersome to work with. It's a lot like telling time…

There are sixty seconds in a minute (60" = 1') and
There are sixty minutes in a degree (60' = 1°).

Keeping in mind a few easy conversions between seconds and decimal minutes will help when working with maps that use degrees, minutes and seconds.

15 seconds is one quarter of a minute or 0.25 minutes
30 seconds is one half of a minute or 0.5 minutes
45 seconds is three quarters of a minute or 0.75 minutes

Degrees and Decimal Minutes

DDD° MM.MMM'
32° 18.385' N 122° 36.875' W

This is the format most commonly used when working with electronic navigation equipment.

Decimal Degrees

DDD.DDDDD°
32.30642° N 122.61458° W
or +32.30642, -122.61458

This is the format you'll find most computer based mapping systems displaying. The coordinates are stored internally in a floating point data type, and no additional work is required to print them as a floating point number.

Often the N-S and E-W designators are omitted. Positive values of latitude are north of the equator, negative values to the south. Watch the sign on the longitude, most programs use negative values for west longitude, but a few are opposite. This saves a lazy western hemisphere programmer from having to type in a minus sign before most of their longitude values.

Which format should you use?

First off, if you are working with other people who have agreed upon a format to use, then you should probably use that format.

Next, you will want to look at the maps, lists of coordinates, and any software you may be using. If you can find a consistent format among them, your work will be easier.

You can set your GPS to display any one of these three formats. Locations can be entered into the GPS with the selected format, and then by switching the display format setting, viewed in a different format.

I frequently choose to use the Degrees and Decimal Minutes format, even though the USGS maps I'm using are marked in Degrees, Minutes and Seconds. The markings on the map are all at either 0, 15, 30, or 45 seconds. By remembering the "quarter minute conversions" of 0.00, 0.25, 0.50, and 0.75, I can quickly do the conversions in my head.

Our thanks to John Carnes of MapTools for use of his copyrighted material
http://www.maptools.com/index.html