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Diving Deeper: Episode 14 (July 29, 2009) —
What is Land Cover Data?

HOST: Welcome to Diving Deeper where we interview National Ocean Service scientists on the ocean topics and information that are important to you! I’m your host Kate Nielsen.

Today’s question is….What is Land Cover Data?

Land cover data documents how much of a region is covered by forests, wetlands, impervious surfaces, agriculture, and other land and water types. By comparing land cover data and maps over a period of time, users can also document land use trends and changes.

To help us dive a little deeper into this question, we will talk with Nate Herold on land cover data – what it is, why it is important, and how we collect it. Nate is a Physical Scientist with the NOAA Coastal Services Center where he leads up the Coastal Change Analysis Program and NOAA’s land cover mapping activities. Hi Nate, welcome to our show.

NATE HEROLD: Thanks Kate, it’s great to be here.

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: Why is it important to have this kind of information on land cover?

NATE HEROLD: Well, it’s difficult to make a management decision related to the natural landscape when you don’t have a very good picture of what that landscape looks like. Land cover maps provide that information. And, more importantly, multiple dates of land cover allow one to see how the landscape has or is changing. This allows for an evaluation of past management decisions, and also gives users the ability to gain insight into the possible effects of their current decisions before they implement them. Either way, the result is a more informed, hopefully better, decision in the present. And that is a must if we want to keep our coasts healthy as the U.S. population in these areas continues to grow.

HOST: Who typically uses or requests land cover data?

NATE HEROLD: Kate, we get a wide range of requests and interest in land cover information. It ranges from very technical folks who are interested in using it their own specific studies to very non-technical users who simply want to know what the lay of the land is for their area of interest; what’s there or what used to be there that isn’t anymore. 

In fact, we’ve been increasingly surprised and thrilled with the amount of non-technical users that are thinking about land cover data and how it can be used to help them in their decision making.

HOST: Nate, how do coastal officials use land cover data and maps?

NATE HEROLD: There are so many ways that officials can and are using land cover data and maps. We actually have a hard time keeping up with it all.

These maps are used to assess urban growth and model water quality issues, predicting and assessing impacts from floods and storm surges, tracking wetland losses and potential impacts from sea level rise, prioritizing areas for conservation efforts or purchases, and in general comparing land cover changes with effects in the environment or to connections in socioeconomic changes such as increasing population. It’s quite a long list and by no means exhaustive.

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.

HOST: Nate, that’s great that this data can be turned around so quickly even for large areas, coastal areas, like you’re saying for Washington and Oregon. Is it expensive to produce?

NATE HEROLD: It can be. There is a cost associated with both the imagery that might be used as well as taking that imagery, interpreting it, and producing the actual map. The interpretation is typically the more expensive piece, and there can be a pretty steep learning curve for folks who’ve not been involved in that type of development before. Cost sharing and partner opportunities are always something that we’re looking for and something I would encourage anyone interested in developing land cover data to explore. It’s almost always easier and cheaper to change something about a standard data set to suit your specific needs than to start something from scratch on your own. 

It’s important to note that such partnering and the use of standardized data leads to more consistent data. Data that can be used outside of one individual application and that can be used to compare one area to another – the coasts of New England to the Gulf of Mexico for example. Something that cannot be done if everyone’s data is produced differently. We’ve found that it saves a lot of money when people can work together to produce one data set instead of producing two or three.

HOST: Well, that definitely makes sense and it sounds like partnerships would be a good thing to be able to work and collect this data. What is the role of the National Ocean Service in collecting land cover data?

NATE HEROLD: NOAA’s land cover work is housed under the Coastal Change Analysis Program or C-CAP. This program has been in existence with NOAA since 1995, and currently resides at the NOAA’s Coastal Services Center, which is part of the National Ocean Service.

The program is focused on creating a consistent product that can be compared through time and between different locations, and that can serve a wide range of applications and uses. I know I mentioned this before, but this is really a distinction between our program and many other land cover datasets. With a standard format and our accuracy specifications, we can really compare different areas or the same area through time, and have it be a real ‘apples to apples’ comparison.

NOAA works closely with the U.S. Geological Survey and several other federal and state programs as well as the private sector to collect this information. All of the data that we produce is incorporated into the National Land Cover Database. We consider the Coastal Change Analysis Program the coastal expression of these national products. This saves the U.S. Geological Survey money because they don’t have to develop data in our coastal areas, and it provides the nation with one comprehensive land cover.

HOST: Nate, as the name, Coastal Change Analysis Program, implies, it sounds like the program focuses mainly on the coastal zone or coastal area? What exactly does this cover?

NATE HEROLD: That’s correct Kate, though our definition of coastal is typically a bit more inclusive than most folks would think. We cover the areas that are defined as coastal through the coastal zone management act, all coastal counties, and the watersheds that drain directly into coastal waters, so the immediate coasts. 

But we typically go a bit further inland than that. We’re trying to capture not only the coastal features and their changes, but all of the areas and changes upstream or uphill that are likely to affect the quality of those coastal areas or the downstream habitats. In many areas of the country, the area that we cover can be up to 100 miles inland. We cover a little bit more than half of the state of South Carolina and we map all of New England for example.  

HOST: Great, so it does sound like the coastal area still covers a lot. Nate, what percentage of our coastal areas in the U.S. currently have land cover data?

NATE HEROLD: Kate, most coastal areas of the U.S. are currently covered. And we’re working to make that true for all areas by filling in some of the gaps that we currently have in the U.S. Virgin Islands and the Pacific Territories of Guam, the Commonwealth of the Northern Mariana Islands, and American Samoa. This is the first time that these territories will be covered as part of a national effort and that’s something that NOAA is proud of.

That work is slated to be complete by the end of 2009, and once it is, every coastal area will have at least one date of consistent land cover available. That includes Alaska which, while isn’t currently covered by NOAA, was mapped through our partners at the U.S. Geological Survey.

HOST: How often are the land cover maps updated?

NATE HEROLD: NOAA’s vision is that these maps would be updated every five years. We haven’t quite hit that vision for every coastal area. For example, Alaska, the Caribbean, and portions of the Pacific Islands only have one date, or they’re being updated on a 10-year cycle. 

But in the lower 48 every area currently has at least two dates – a 1996 and a 2001. And we’re about 60 percent complete on our 2006 update cycle. That work will be done in 2010 and then the plan is to start the whole cycle over again. And then do the same thing in 2015. 

Also, there are a few areas where we’ve worked with regional or state partners to start looking backwards in time, creating land cover for dates in the early 90s or mid 80s. We’d like to do more of that type of work. It’s very interesting to have that longer view.

HOST: What trends, if any, did we find from the initial release of the national maps?

NATE HEROLD: Well, we’ve seen a couple of interesting things. One is the sheer amount of change that is occurring in coastal areas. We documented that an area roughly the size of the state of Maine changed in some way between 1996 and 2001. That’s just five years and Maine is not a small state. Most of the change was associated with silviculture activities, or the cycle of forest management where trees are harvested and the area goes through the regeneration of grass, scrub land, and eventually back to forest. This trend is most obvious in the Southeast and the Pacific Northwest.

We also noticed a significant amount of development. We documented an increase in developed area that was roughly equivalent to 7.5 New York cities. Again, pretty significant for just a five-year time period. This was primarily lower-density development. The development most commonly associated with residential neighborhoods in suburbs and urban fringes. For the most part, this growth has been fairly focused in the Southeast and Gulf coasts, and around the outside of major urban centers such as the Chicago suburbs. In fact, we saw that 10 percent of the coastal counties actually accounted for more than half of all of this new development. That’s 85 counties out of 850 that account for half of all this growth.

HOST: Nate, this is great data and sounds like a comprehensive review of our nation’s coastal areas. Land cover data is extremely valuable when you consider all of the information we are able to get by comparing and assessing trends from these maps. Why is this type of trend analysis important?

NATE HEROLD: Kate, trend data identify if the area’s covered by a particular land type and whether it’s increasing, decreasing, or remaining unchanged. Comparing trends may help us determine cause and effect relationships such as an increase in urban area causing a reduction in forest area, or that the two of these cause decreases in downstream water quality, or that the decrease in downstream water quality impacts essential fish habitat.

This information can also be used to predict future changes in the landscape and with that information coastal managers can better plan how to manage their coastal resources.

HOST: Nate, have there been any economic benefits of this kind of land cover data to state programs?

NATE HEROLD: Sure, the state of Maine is a really good example. They needed a way to map their land cover. And they needed some modifications that the Coastal Change Analysis Program did not supply. They were interested in determining water quality criteria and to calculate health risks for long-term management. They’d been using data that was over 14 years old and understandably out of date. 

They partnered up with NOAA and some of our private industry partners, they leveraged our efforts, and were able to simply make some tweaks to our data as opposed to doing all of the work themselves from scratch. In the end, this saved the state approximately $300,000, that’s almost a 50 percent savings on their part, and they were able to get the data that they needed – something they couldn’t have afforded to do on their own.  

We’ve also had some very good partners with other states and regional programs such as the State of Washington’s Department of Ecology and the Chesapeake Bay Program, where we’ve supplied technical assistance to their effort in order to ensure that the data they were producing would meet national standards as well as their own needs. In that way, everyone ends up working towards the same goal, everyone saves time and money, and we all have a consistent product.

HOST: That’s a great case study – a great example – of really good benefits to a state program. Thank you Nate for all of this helpful information and examples to define land cover data better for us today. Do you have any final closing words for our listeners?

NATE HEROLD: Just that I appreciated the opportunity to talk to you and the listeners about coastal land cover and change. Thank you.

HOST: Thanks Nate for joining us on today’s episode of Diving Deeper and talking more about land cover, why it is important, and how we collect it. To learn more about land cover maps or to access land cover data, please visit

That’s all for this week’s show. Please tune in on August 12th for our next episode on currents.