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# Making Waves: Episode 74 (May 5, 2011)

You're listening to Making Waves from NOAA's National Ocean Service. I'm your host, Troy Kitch.

Do you remember filling out the 2010 Census form from the U.S. Census Bureau? Well, today, we're going to tell you about one small — but very interesting — piece of information gleaned from combining together all the census data from our nation's population.

Every ten years, when we do the census, the numbers are crunched to figure out exactly where the center of the U.S. population falls. It's a point called the Centroid. Well, the Centroid for the 2010 U.S. population has been calculated ... and you'll have to stay tuned to find out where it is.

We're joined today by telephone with Dave Doyle, chief Geodetic Surveyor with NOAA's National Geodetic Survey — the office that's responsible for placing a geodetic survey disk at the precise point called the Centroid. And there is perhaps no better person to tell us about this, because Dave has been involved with placing a survey marker at the center point of the U.S. population every ten years since 1980.

I first asked Dave to explain how the Census calculates the centroid for population. He said to think of a nice rectangular-shaped state like Colorado. If you imagine Colorado as a perfectly flat plain — without all the mountains and valleys — and you put it on a map, that place where this rectangular shape balances perfectly on a point is the centroid. The process that the Census Bureau uses to figure out the centroid for the U.S. population is more complicated than this, but it's the same idea...

[Dave Doyle] "But to sort of encapsulate the whole process — if you thought of the United States — and this includes Alaska and the territories — if you thought of it as a flat plain, you put it on a map, and had it on a nice hard piece of cardboard, and if all of the population weighted exactly the same — which of course we don't — but if we did, where would the country balance the population at one specific point in time? Because obviously the population is changing day to day — but based on the data collection that the Census has made relative to the 2010 cycle, where would that center of population be? Where would the country kind of balance."

To get at why this is so useful, you have to consider that the centroid is something the Census Bureau has been tracking for a long, long time. Every ten years, we get another point to plot on a U.S. map. Connect the dots, and you get a snapshot of how our population is shifting over time.

[Dave Doyle] "What you notice is that there's this very distinct trend, as the country built, the people moved to the West and the line of the center — the various centers from, oh, roughly 1790 when it was in Kent County, MD, to about 1920 or so when it's in Indiana, is almost a straight line to the West. Beginning around 1930, the trend now starts to go to the Southwest, so we see the influx of people moving to places like Texas, and New Mexico, and California, so that Southwestern trend is quite apparent, just looking at where the centers of population are."

Dave said the National Geodetic Survey has been involved with this effort since 1960, when the Census Bureau asked the predecessor to the Survey to place a geodetic survey monument at or very near the exact coordinates of the centroid.

[Dave Doyle] "That is, to put a very accurate longitude and latitude on that marker as part of the national reference framework that we've been responsible for since 1807. And so since 1960, every ten years, following the computation of the center of population, they provide us with those values and then we would send a field team out to that location and find where that coordinate is on the ground, and then actually place a geodetic control marker there and position it very accurately and then integrate that data into the network of other survey control points that we refer to as the National Spatial Reference System."

The National Spatial Reference System is a huge network of about 1.5 million monuments, or bench marks, around the nation. The latitude, longitude, and height of each of these reference points form the foundation for all of our geographic mapping needs — for things like nautical charting, aeronautical charting, and topographic mapping. The National Geodetic Survey tracks all of these reference points, and the agency and its predecessors have been doing this since Thomas Jefferson founded the Survey of the Coast over 200 years ago. Dave said that since the beginning, the Survey has used the most advance technology available to form this geographic reference system. But he said there's been an incredible transformation over the last 20 to 30 years that makes this reference system more relevant to more people than ever before — the advent of the Global Positioning System.

[Dave Doyle] "Certainly we see the impact of that today in just the most rudimentary forms. Almost everybody has some sort of positioning capacity in smart phones, or iPads, or iPhones, what have you in their cars and trucks and on their bicycles and on their wristwatch. So the ability for the average individual to position themselves has become an important part of our national infrastructure — the ability to get somewhere very quickly and very accurately. And at the heart of that, the capacity to do that accurately, is this rather invisible piece of our infrastructure that we refer to as the National Spatial Reference System."

Now for the big moment you've all been waiting for ... drumroll please ... where is the 2010 Centroid of the U.S. population going to be placed?

[Dave Doyle] "The Centroid is in a little town called Plato, MO. It's about an hour and a half, and hour and twenty minutes, sort of Southwest of Rolla, MO."

Dave led a team out to the site for reconnaissance in April so they could pin down the exact location. It's a pretty small place.

[Dave Doyle] "As we were driving into the town, there's a nice little sign that has the name of the town, and I believe it said the population was like 78 or 79, and almost immediately, a couple of folks in the car from Census said 'Oh, we've got to change that,' It's now like 110 or 112, I forget the exact number, but it's a pretty small community, and they're pretty excited about this. And that's a great part of it. It brings home these rather large and somewhat vague concepts, brings it to these communities where it makes them understand how important everybody is in the context of the whole country, and I think it's wonderful to be a part of that."

A formal dedication ceremony sponsored by the Census Bureau is scheduled for ... or was on (depending on when you're listening to this podcast) ... May 9th at 1p.m. in Plato, Missouri. Dave will be there, along with the Director of the National Geodetic Survey, and the Director of the Census Bureau. And so will probably a good portion of the population of Plato, Missouri.

For Dave, it'll be a very special event. He participated in his first centroid of the U.S. population event in 1980, and he's been in charge of the event for the National Geodetic Survey since 1990. The 2010 event will be his last as a NOAA employee.

[Dave Doyle] "I like to think about this as a great opportunity to highlight the relationship between Census and NOAA as part of the Department of Commerce, and the legacy that we've created there. I think it's a wonderful cooperative effort. It's been a real pleasure for me over the last roughly 35 years to be a part of this effort."

That was Dave Doyle, chief Geodetic Surveyor with NOAA's National Geodetic Survey

And that's all for this episode.

If you have any questions about this week's podcast, about the National Ocean Service, or about our ocean — or if you have an ocean fact you'd like answered — send us a note at nos.info@noaa.gov.

This is Making Waves from NOAA's National Ocean Service.

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