How to convert Geographic Coordinates
Navigation Tools 1.1
Life Skills:
 Thinking: problem solving, leaning to learn, critical thinking
 Managing: planning/organizing, keeping records
Standards/Objectives:
 How to use geographic tools and technologies to acquire, process and
apply information from a spatial perspective
Requirements:
 Computer with internet connection
 Waypoint data
 www.geocaching.com
 Activity Lesson, “Hands On, How to Convert Geographic Coordinates.”
ASK
Did you know that there is more than one format for recording latitude and
longitude? To show data on maps, latitude and longitude coordinates are
recorded on spreadsheets like Excel or notepad programs and downloaded to
the map. If all data isn’t in the same format, waypoints will not show up on your
map.
What if you have gathered data in more than one coordinate format? How can
you convert all data to one format?
Three types of geographic coordinate formats
All of the formats below refer to the same location!!!! The latitude and longitude
are represented differently in different formats
DD Decimal Degree – eg – 39.500
DMS Degrees Minutes Seconds – eg – 39 degrees 30 minutes 0 seconds
(looks like 39°30.0)
DM Decimal Minutes eg – 39 degrees 30.0 minutes
INVESTIGATE
Converting your waypoint data from Degrees Minutes Seconds (DMS) to Decimal
Degree (DD) format (or vice versa) is easy and can be done automatically on the
internet as shown in the accompanying activity lesson, “Hands On, How to
Convert Geographic coordinates”. Conversion may also be figured manually with
this formula: (D + M/60 + S/3600). It is suggested that you try both methods.
(Please see the excellent information from Wikipedia (Jan 2009) about
coordinate formats that is included at the end of this document.)
CREATE
The accompanying activity lesson, “How to convert geographic coordinates” will
show you how to quickly convert your data. Several web sites can do this for
you, but www.geocaching.com is one of the easiest and is used in the activity
lesson. The activity shows step-by-step instructions and graphics. This lesson
shows how to convert to Decimal Degree (DD) geographic coordinates for
layering waypoints onto maps (The DD will look like: 38.72888 and -87.8712).
DISCUSS
After trying the online and the manual method of conversion, which do you
prefer?
Did you know you can reset your coordinate format on your GPS receiver?
REFLECT
How can your new conversion skills help you?
The excerpts between the dashed lines below are from Wikipedia (Jan.
2009) and explain in more detail the principle of these coordinate systems.
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Decimal degrees From Wikipedia, the free encyclopedia
Decimal degrees (DD) express latitude and longitude geographic coordinates as
decimal fractions and are used in many Geographic Information Systems (GIS),
web mapping applications such as Google Maps, and GPS devices. Decimal
degrees are an alternative to using degrees, minutes, and seconds (DMS). As
with latitude and longitude, the values are bounded by ±90° and ±180° each.
Positive latitudes are north of the equator, negative latitudes are south of the
equator. Positive longitudes are east of Prime Meridian, negative longitudes are
west of the Prime Meridian. Latitude and longitude are usually expressed in that
sequence, latitude before longitude.
Accuracy
A value in decimal degrees to an accuracy of 4 decimal places is accurate to 10
meters at the equator. A value in decimal degrees to 5 decimal places is
accurate to 1 meter at the equator. Because the earth is a spheroid and not flat,
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the accuracy of the longitude part of the coordinates increases the further from
the equator you get. The accuracy of the latitude part does not increase.
Example
The decimal degree representation of the location of the United States Capitol is
"38.889722°, -77.008889°". In most systems, such as Google Maps, the degree
symbol is omitted and thus the coordinates are expressed as "38.889722, 77.008889".
Conversion from DMS to DD
With DMS, the location of the United States Capitol is "38° 53' 23" N, 77° 00' 32"
W". A DMS value is converted to decimal degrees using the formula (D + M/60 +
S/3600). Thus the decimal degree representation of "38° 53' 23" N, 77° 00' 32"
W" is "38.889722°, -77.008889°", as shown above in the example.
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Note to proofreader: EVERYTHING BETWEEN THE
DOTTED LINES IS COPIED ALMOST DIRECTLY FROM
WIKIPEDIA, WITH MINOR CHANGES IN FONT COLORS
AND REMOVAL OF HOTLINKS. THESE ARE THE
SIMPLEST AND BEST EXPLANATIONS FOR THIS
ACTIVITY THAT I HAVE FOUND, AND WE WILL NEED
TO CHECK INTO COPYRIGHT IF USED. Barb
Related Weblink:
http://www.fcc.gov/mb/audio/bickel/DDDMMSS-decimal.html This Federal
Communication Commission site. This utility permits the user to convert latitude
and longitude between decimal degrees and degrees, minutes, and seconds.
Authors: Barb Roberts, Youth Development Educator, University of Illinois
Extension, Lawrence/Richland Unit. and Dennis Bowman, Extension Educator,
Crop Sciences, University of Illinois Extension, Champaign Extension Center
Date: March 16, 2009
Sources: Dennis Bowman; Joseph Kerski, ESRI; Wikipedia Jan 2009
University of Illinois  U.S. Department of Agriculture  Local Extension Councils Cooperating
University of Illinois Extension provides equal opportunities in programs and employment. If you need a reasonable
accommodation to participate in this program, please contact the county Extension office.
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