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Diving Deeper Shorts: Episode 9 (February 10, 2011) - Land Cover Data

HOST: Today on Diving Deeper Shorts, we revisit our previous interview on land cover data with Nate Herold from the NOAA Coastal Services Center.  

Let's listen in.

HOST: Nate, what is the difference between land use and land cover?

NATE HEROLD: Well, that's a good question, Kate. The two terms are often used interchangeably, but as you stated a second ago, land cover captures what actually covers the land - forest, grassland, impervious or paved surfaces, for instance. Land use, on the other hand, documents how humans are using those landscapes - whether the areas are residential, commercial, or industrial development. The same types of cover can be managed or used very differently.

HOST: So Nate, how does land cover data work? How are we able to document how much of a region is made up of different land and water types such as forest and wetland?

NATE HEROLD: Land cover maps are most often created using remotely-sensed data and that can come from either satellites or aircraft imagery. The information within the imagery goes beyond just a pretty picture. It's like a giant spreadsheet of digital numbers where each cell in the spreadsheet represents a square area on the ground or a pixel. How red, how blue, how green features are are all contained within that spreadsheet. And the data can be used to tell us what types of land cover are present in each of those pixels.

We interpret those pixels and then it becomes a map. This can be done through human interpretation where somebody would draw a line and label a feature by hand, or with the aid of some fairly sophisticated computer software. It is often said that this type of analysis is as much an art as it is a science.

HOST: How long does it take to produce one of these data sets?

NATE HEROLD: Well, that depends on a number of things like the size of the area that you're interested in or the types of land cover categories. But from our experience, it always takes a little bit longer the first time. At the Center, we initially focused on a standard process for collecting and processing the imagery. And now that we have that process in place, the time to produce new data and maps is even faster. 

When we created our first baseline dataset we had to map everything, every pixel. Now we only remap the areas that have changed since that baseline map was produced. This keeps the unchanged areas consistent and we save time and money by not having to reinterpret areas that we don't have to. 

NOAA has a great team here at the Center that is responsible for this work. We can turn around an update for the coastal areas of Washington and Oregon, for example, in about four to six months. And we can typically complete three to four similar size regions every year. And, as I said before, we work hard to ensure that we complete the entire country within five years so that we can start the whole process again.

That's all for today's Diving Deeper Shorts, where we highlight a few minutes of your favorite Diving Deeper episodes.

Want to learn more? Go to and select the July 2009 podcast archive to listen to the full interview with Nate Herold on land cover data.

You can catch the next episode of Diving Deeper on February 24.