MAKING LATITUDE and LONGITUDE DATA WORK for YOU
How
can I use latitude and longitude information?
Here are some simple steps for using latitude and longitude (L/L)
information in everyday activities. The
material below is organized to first give you the information you need to put
L/L data to work. Additional
definitions and explanations are available by clicking on the highlighted terms
in this discussion.
There
are two principle methods for using L/L information in everyday
activities. One involves using your GPS unit to home-in on a pair of L/L
coordinates. The second method is based
on your selecting a location or point for which you know the L/L and making
measurements to a second location using the L/L of the second location. Each method is described below.
Finding
a Location or Point on Earth by Using Your GPS Unit:
This
is the simplest method for finding a location or point on earth. It involves trial-and-error. All you need is your hand-held GPS
unit. A map can be useful if the location
or point you are trying to find is miles away.
If you are looking for a specific location or point within a cemetery,
for example, a plain piece of paper can substitute for a map. In either case, the steps are the same. A compass can come in handy but it is not
necessary if the sun is shining brightly enough to cast a clear shadow.
The steps below apply to the northern hemisphere (equator to the north
pole) and the western hemisphere (Greenwich, England and west through 180
degrees longitude).
1.
Go to a location that is as close to the unknown location that you are
seeking as you can. If you are looking
for a building or cemetery (for which you have the L/L) in a county, for
example, go first to the county where you believe the building or cemetery to
be. If you have additional information
such as the building or cemetery is close to a specific village, go to that
village to start your search. If you
are looking for a grave (for which you have the L/L) in a specific cemetery, go
to that cemetery.
2.
Select a starting point a point from which you will start your
search. It can be anywhere you
choose. Mark this point on your map or
piece of paper. Turn on your GPS and
take a reading at this point. Record
your latitude and longitude by the starting point.
3.
Compare the L/L of your GPS reading at your starting point with the L/L
of the location you are trying to find.
a.
If the latitude of the location you are seeking is greater than (a
higher number) the latitude of the starting point, you will need to go north to
reach the location you are seeking.
b.
If the latitude of the location you are seeking is less than (a lower
number) the latitude of the starting point, you will need to go south to reach
the location you are seeking.
c.
If the longitude of the location you are seeking is greater than (a
higher number) the longitude of the starting point, you will need to go west to
reach the location you are seeking.
d.
If the longitude of the location you are seeking is less than (a lower
number) the longitude of the starting point, you will need to go east to reach
the location you are seeking.
4.
Move to a new location based on the results of your comparison in item
3 above. Take a second GPS reading and
again apply the criteria given in item 3 above.
5.
Repeat steps 2 and 3 until you arrive at the L/L readings of the
location you are seeking. You are done.
Finding a Location or Point on Earth Using a the L/L of a Known Point and the L/L of the Point You are Seeking :
For
this method you will NOT need a GPS although it can be useful to confirm your
findings. You will need a tape-measurer
marked in feet and inches and either a compass or a sunny day.
1.
Go to a point for which you know the L/L. This will be your starting point. This starting point might be a building, courthouse, cemetery, or
other location if the location you are seeking is miles away. If you are seeking an unknown location
(maybe a grave) in a cemetery, the starting point might be a corner of that
cemetery, the front door of the church, or even another grave marker. The only criterion is that you know the L/L
of your starting point.
2.
You need to know two things to get from your starting point to the
location that you are seeking. These
two things are the direction to go and how far to go in that direction. You will need a compass or the shadow formed
by bright sunlight to know which direction to walk or drive. The rules for deciding which direction to go
are the same as for item 3 above for using the GPS.
a.
If the latitude of the location you are seeking is greater than the
latitude of the starting point, you will need to go north to reach the location
you are seeking.
b.
If the latitude of the location you are seeking is less than the
latitude of the starting point, you will need to go south to reach the location
you are seeking.
c.
If the longitude of the location you are seeking is greater than the
longitude of the starting point, you will need to go west to reach the location
you are seeking.
d.
If the longitude of the location you are seeking is less than the
longitude of the starting point, you will need to go east to reach the location
you are seeking.
3.
In this method, you may only move due north or south and due east or
west. From item 2 above, you have
determined which direction you need to move from the starting point. You now need to make a simple calculation to
figure out how far you need to go to the east or to the west. First, subtract the longitude of the
location you are trying to find from the longitude of your starting point, or
vice versa (subtract the smaller number from the larger number). To determine how far you need to go from
the starting point in the easterly or westerly direction, multiply the
difference in the degrees by 53.2* to get the number of miles you need to go
from the starting point to the location you are seeking. [Note:
There will never be one full degree of difference between the starting
point and the location you are seeking as long as you are in Monroe County. So this part of the calculation (subtracting
the degrees) will not occur. It is
included here in case you are starting much farther away.] Then, multiply the difference between the
minutes by 4691* to get the number of additional feet you need to go to get
from the starting point to the location you are seeking. Add the miles (this will usually be zero)
plus the feet to get the full distance from the starting point to the location
you are seeking (in the east or west direction).
Now, repeat the calculation above to determine how
far you need to move in the north or south direction. First, subtract the latitude of the location you are trying to
find from the latitude of your starting point, or vice versa (subtract the
smaller number from the larger number).
To determine how far you need to go from the starting point in the northerly
or southerly direction, multiply the difference in the degrees by 69 to get the
number of miles you need to go from the starting point to the location you are
seeking. [Note: There will never be one full degree of
difference between the starting point and the location you are seeking as long
as you are in Monroe County. So this
part of the calculation (subtracting the degrees) will not occur. It is included here in case you are starting
much farther away.] Then, multiply the
difference between the minutes by 6076 to get the number of additional feet you
need to go to get from the starting point to the location you are seeking. Add the miles (from the degrees
calculation, if you are starting outside Monroe County) plus the feet (from the
minutes calculation) to get the full distance from the starting point to the
location you are seeking (in the north or south direction).
4.
Measure the two distances that you have calculated, in the appropriate
directions, to arrive at the point you are seeking.
* These factors can be applied anywhere
within Monroe County or near the 40 degree parallel line of
latitude. Other factors should be
applied at different degrees of parallel.
Click here for a list
of factors for other parallels.
Latitude
are imaginary lines on the surface of the earth that includes the equator and
measures the distance in degrees, minutes, and seconds between the equator
(zero degrees) and the north or south pole (90 degrees). Lines of latitude in the northern hemisphere
are identified as north latitude while latitudes in the southern hemisphere are
identified as south latitude.
Longitude
are imaginary lines on the surface of the earth that run from the north pole to
the south pole. Lines of longitude are
also measured in degrees, minutes, and seconds with zero degrees longitude (the
prime meridian) being arbitrarily set as passing through Greenwich, England, a
borough of London. Lines of longitude
are numbered.
Click here for more detailed information about
L/L.
GPS
stands for Global Positioning System. A
GPS unit is a hand-held device about the size of a cell phone that measures the
latitude, longitude, and elevation (in feet above sea level) at the point where
it is located. Click
here for more details about the GPS, its history and use.
It
is important to know the direction of North to the process of finding a
location or point using either a GPS unit or calculating it from existing L/L
data. The compass is one of the best
tools for this. Most GPS units have a
compass that determines North from the
data it receives from satellites. One
of the most useful ways of determining the points of the compass rose (north,
south, east and west) is to measure it using bright sunlight. This method is described below.
1.
Find an object that is securely attached to the earth. This can be a stick pushed into the ground
(ideally 3 or 4 feet long), an existing fence post, even a well defined point
on a grave marker. Ideally, it should
be thin and/or come to a point so that in bright sunlight it will cast a well
defined shadow on the ground.
2.
Place a short stick or other marker in the ground at the point where
the shadow of the well defined marker strikes the ground.
3.
Allow several minutes to pass (minimum of 10 minutes). Again locate where the shadow of the well
defined marker strikes the ground.
Place a second stick or other marker in the ground at this point.
4.
A line drawn between the two sticks or markers lies true east and
west. The direction from the first
stick to the second stick is the direction East. Adding additional sticks or markers over a period of an hour or
so can greatly improve the east-west line.
This
method of watching the movement of a shadow works best in mid-morning and
mid-evening. While it still works at
high noon, it is frequently more difficult to track the movement of the shadow.
The
conversion factors given above are correct for Monroe County, Ohio and other
places on or near the 40th parallel of latitude. For other parallels use the conversion
factors in the table below.
Interpolations between parallels can be done successfully.
Conversion Factors from Degrees, Minutes and Seconds to Miles
and Feet
|
Degrees of North Latitude |
Conversion Factor for One Degree
of Longitude (in miles) |
Conversion Factor for One
Minute of Longitude (in feet) |
Conversion Factor for One
second of Longitude (in feet) |
Approximate Locations at
this Degree of Latitude |
|
30o |
59.96 |
5274 |
88 |
Houston, TX |
|
35o |
56.73 |
4992 |
83.2 |
Albuquerque,
NM |
|
39o 43.6 ** |
53.2 |
4691 |
80.5 |
Monroe
Co., OH |
|
40o |
53.06 |
4669 |
77.8 |
Kansas/Nebraska
Border |
|
45o |
49.00 |
4312 |
71.87 |
Montana/Wyoming
Border |
|
49o |
45.40 |
3995 |
66.59 |
U.S./Canada
Border |
|
50o |
44.55 |
3920 |
65.34 |
|
|
55o |
39.77 |
3500 |
58.33 |
|
|
60o |
34.67 |
3051 |
50.85 |
|
** Approximate latitude at middle of Monroe County, Ohio
Following is an example of how to find a location or
point on Earth using the L/L of a known point and the L/L of the location or point
that you are seeking. For this example,
we will use data from the Buchanan Cemetery Cemetery
inventory and chart. The starting point for the search will be
the northeast corner of the cemetery that has been identified as point A on
the chart. The L/L of point A is given
as 39o 46.101 North Latitude and 81o 10.770 West
Longitude. We will seek the
measurements and the direction to the grave marker of Deloris & Bruce
Strickling. The coordinates of this
marker is given as 39o 46.051 North Latitude and 81o
10.777 West Longitude.
Step 1 of the guidance above tells us that if If
the latitude of the location you are seeking is less than the latitude of the
starting point, you will need to go south to reach the location you are seeking. Step 1 further tell us that if If the
longitude of the location you are seeking is greater than (a higher number) the
longitude of the starting point, you will need to go west to reach the location
you are seeking. So, we now know the
directions we will move to get to the Strickling marker. We will move south then west. [Actually, it does not matter which order we
make these two moves. We could just as
well first move west then south.]
We now need to calculate how far south and how far
west we should move. Let s first
subtract the smaller longitude from the larger longitude. Thus, we subtract 81o 10.770
from 81o 10.777 for a difference of 0.007 minutes. To convert the answer that is in minutes, to
feet, we are instructed to multiply by 4691 which gives us 32.8 feet or 32 feet
and 9 inches.
Next, lets subtract the smaller latitude from the
larger latitude. In this case, we
subtract 39o 46.051 from 39o 46.101 to get 0.05 minutes. To convert the answer that is in minutes, to
feet, we are instructed to multiply by 6076 which gives us 303.8 feet or 303
feet and 9 inches.
So, starting from our starting point of A we need
to measure south 303 feet and 9 inches; then, measure west 32 feet and 9 inches. This looks to be about right when we look at
the Strickling marker (marker # 100) on the chart of the Buchanan Cemetery.
Now, wasn t that easy?
Before you decide to place a bet on the accuracy of
our answer, however, you need to be aware of two potential sources of error. The GPS readings for point A shows an
accuracy of 14 feet. The GPS reading
for the Strickling marker shows an accuracy of 15 feet. While these are relatively small errors,
they could combine for a possible error of 29 feet. The second potentially significant source of error is in the
measurement of a true north-south line from the starting point. A slight error in laying out this true
north-south line could make a big difference 303 feet away. This error can be minimized by the use of a
transit or other means of laying out a true north-south line. In practice this source of error can be kept
to within a few inches.
Provided by Richard
Harrington
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