Using GPS Coordinates

This site uses GPS coordinates to mark individual graves and create maps of cemeteries. However, as good as GPS is, it's not perfect. If you use the maps and coordinates used on the individual cemetery pages, here are some things to be aware of and to understand.

Differences in the Datums

A datum is a set of reference coordinates from which tools such as maps and coordinates are calculated. Each datum is, essentially, its own rulebook for establishing how to read a map's coordinates.

Think of it this way: each language has its own dictionary. If you wanted to find the meaning of the word "kartoffel," looking in the English dictionary would do you no good, as "kartoffel" is a German word. (An English speaker would call a "kartoffel" a "potato.")

Each map is built using a datum, just like each language is built of words from its own dictionary. To understand the map correctly, you need to know which datum it is built upon.

If you think that using any datum to locate your coordinates is "good enough," well, you could find yourself miles from where you'd like to be.

The most common datums used in North America are NAD 27, NAD 83, and WGS 84. All of my maps and coordinates are based on the WGS 84 datum. To best use my coordinates, makae sure your GPS is using that same datum. Most currently available GPS devices come pre-set to use this datum by default. WGS84 stands for the World Geodetic System of 1984, and is the only world referencing system currently in place.

Differences in Coordinate Systems

To further complicate matters, each of the datums can be used to create map coordinates in any number of coordinate systems. Each of these systems are used for different purposes, but, there can be large differences in a position if one uses the wrong coordinate system to interpret the position.

To extend the language illustration a bit further, let's say, both people speak English, but, one is from Scotland, and the other person is from Texas. Accents and slang words used by these two people are very different, and can lead to big misunderstandings, even to the point where neither person understands a word the other is saying.

Many coordinate systems use the degrees, minutes, seconds approach to present a GPS coordinate for both longitude and latitude, so, it can be very deceptive as to which coordinate system is being referenced. Again, guessing incorrectly can literally put you a world away from your intended destination.

For my maps and coordinates on this site, I use the UTM (Universal Transverse Mercator) coordinate system. To give an idea of the difference, here's the exact same point in UTM (13 S 405829 4380726) and in Geodetic Longitude and Latitude, N39 47.487 W104 57.618)

Differences Caused by Composites

Sometimes, maps are created from composites of information from different datums. Maps from the internet are often composites, and this means that things can appear shifted by a few feet here or there.

Google Earth, which is used to gather the main map imagery for the galleries you'll see on this site, largely uses the WGS84 datum, but, the images are often pulled from a wide variety of sources. When looking at a map on the internet, assume it is a composite unless it specifically states otherwise or you can find the exact datum for it.

Differences Caused by Physical Location and Conditions

And then there's marking a GPS point itself. Making a GPS point depends on how many satellites are available overhead. The more satellites you get, the better the accuracy of the mark. Holding your unit parallel to the ground and then shifting it around can take your accuracy from within 10 feet, and change it to 25 feet!

Things like densely wooded areas, extremely remote areas, the weather and elevation can all affect your GPS unit's ability to acquire satellites, and change the accuracy of your marks.

Why Bring All This Up?

Because, as much as I'd like the coordinates I take or the maps I create to be perfect and extremely accurate, the system's not perfect, so, items in the galleries will often have marked points up to several feet from where they actually exist in the real place.

However, I aim to get you very close. Close enough that you can look around, and, in a few seconds, locate the spot referenced relatively easily.

Return to Cemetery Records from GPS notes