visualization

Shifting Without Datum Documentation

By Casey J. McLaughlin

Most of us take for granted that latitude and longitude always mean the same place on a map but is that true?  I started thinking about GPS points and how a simple hand held (or my phone) may have an error of +/- several feet.  Now I am wondering if the fuss I make about specifying Datum is worthwhile….

Claudius Ptolemy: The World, 1482 (Wikipedia)

A Datum, defined by Webster’s is generally “something used as a basis for calculating or measuring.”  Ah ha! I had never thought outside of the geographic usage of the word but I find understanding word roots can be quite helpful.  What I really mean is what impact a Geodetic Datum has on latitude/longitude pairs.  A Geodetic Datum is “the reference point for the various coordinate systems used in mapping the earth” (Geography.about.com).  The Earth isn’t perfectly round and geodetic datums form the mathematical basis for modeling our home.

Meades Range Marker, Kansas (geocaching.com)

There are several datums which I see most frequently; NAD27, NAD83, and WGS1984.  The NAD27 (North American Datum 1927) is interesting from a Region 7 perspective because its origin point is a survey point in Kansas – Meades Ranch (approx. 39.224087, -98.542152).   Just for reference, the geometric center of the contiguous U.S. is also in Kansas! Once we began using high precision remote sensing technology, we needed a new datum – NAD83 (North American Datum 1983) was born.  NAD83 has its origin defined by the Earth’s center of mass.  The two systems are different enough that a given latitude/longitude could be several meters off – depending on the distance from the datum!  Today, the World Geodetic System (WGS) 1984 Web Mercator is commonly used – I believe most major web platforms use it.

The main point I’m getting at here is that documenting the coordinate system information of geospatial data IS important.  I have seen more than one dataset come in without proper documentation.  To map it, I have to assume what datum is used – it wasn’t recorded.  Please, if you’re collecting spatial data, don’t complicate it with incomplete information!  Documenting our data collections is vital for using data with confidence and ensuring future data reuse.

For more information on Geodesy and such, check out:

Casey McLaughlin is a first generation Geospatial Enthusiast who has worked with EPA since 2003 as a contractor and now as the Regional GIS Lead. He currently holds the rank of #1 GISer in EPA Region 7′s Environmental Services Division.

Editor's Note: The opinions expressed herein are those of the author alone. EPA does not verify the accuracy or science of the contents of the blog, nor does EPA endorse the opinions or positions expressed. You may share this post. However, please do not change the title or the content. If you do make changes, please do not attribute the edited title or content to EPA or the author.

EPA's official web site is www.epa.gov. Some links on this page may redirect users from the EPA website to a non-EPA, third-party site. In doing so, EPA is directing you only to the specific content referenced at the time of publication, not to any other content that may appear on the same webpage or elsewhere on the third-party site, or be added at a later date.

EPA is providing this link for informational purposes only. EPA cannot attest to the accuracy of non-EPA information provided by any third-party sites or any other linked site. EPA does not endorse any non-government websites, companies, internet applications or any policies or information expressed therein.

Watching the Wind

By Casey J. McLaughlin

Hurricane season is upon us and Isaac has been dumping vast amounts of rain along its path.  In the Midwest we might see the rain aftermath of Hurricanes but as far as I know, we don’t have any regular Hurricane Drills.  We do, however, have Tornado Drills – quick, run to the basement!  When I think of a tornado, I think of wind, wind, and more wind.

hint.fm/wind August 29, 2012

In that vane (pun intended) check out the great visualization work at http://hint.fm/wind/.  The authors created a “personal art project” with surface wind data from the National Digital Forecast Database.  I often reflect on the maps I’ve made and I think they lack a certain artistry that made me love maps in the first place – hello National Geography.  This wind map, to me, is the best of both “big” data and artistic visualization.  The hint.fm web map visualization presents a tremendous amount of data in an incredibly artistic way – AND ITS ZOOMABLE?

hint.frm/wind August 29, 2012

There are many more data visualization and analysis tools available.  They may have more meaningful information but I still love the majesty of the movement.  Just as a side note, NASA has a similar visualization using surface currents.  View the youtube video here:

Casey McLaughlin is a first generation Geospatial Enthusiast who has worked with EPA since 2003 as a contractor and now as the Regional GIS Lead. He currently holds the rank of #1 GISer in EPA Region 7′s Environmental Services Division.

Editor's Note: The opinions expressed herein are those of the author alone. EPA does not verify the accuracy or science of the contents of the blog, nor does EPA endorse the opinions or positions expressed. You may share this post. However, please do not change the title or the content. If you do make changes, please do not attribute the edited title or content to EPA or the author.

EPA's official web site is www.epa.gov. Some links on this page may redirect users from the EPA website to a non-EPA, third-party site. In doing so, EPA is directing you only to the specific content referenced at the time of publication, not to any other content that may appear on the same webpage or elsewhere on the third-party site, or be added at a later date.

EPA is providing this link for informational purposes only. EPA cannot attest to the accuracy of non-EPA information provided by any third-party sites or any other linked site. EPA does not endorse any non-government websites, companies, internet applications or any policies or information expressed therein.