definition latitude and longitude

Latitude

Lines of latitude measure north-south position between the poles. The equator is defined as 0 degrees, the North Pole is 90 degrees north, and the South Pole is 90 degrees south. Lines of latitude are all parallel to each other, thus they are often referred to as parallels.

The memory rhyme I use to help remember that lines of latitude denote north-south distance is:

"Tropical latitudes improve my attitude"

One degree of latitude is

60 nautical miles, 69 statute miles or 111 km.

One minute of latitude is

1 nautical mile, 1.15 statute miles, or 1.85 km.

Longitude

Lines of longitude, or meridians, run between the North and South Poles. They measure east-west position. The prime meridian is assigned the value of 0 degrees, and runs through Greenwich, England. Meridians to the west of the prime meridian are measured in degrees west and likewise those to the east of the prime meridian are measured to by their number of degrees east.

The memory rhyme I use to help remember that lines of longitude denote east-west distance is:

"Lines of LONGitude are all just as

LONG as one another."

With this saying in my mind, I picture all of the longitudinal meridians meeting at the poles, each meridian the same length as the next.

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.