Open Access to USGS DEM data... Myth Or Reality? You Be The Judge
Written by Glenn Letham (GISuser editor)
21 March 2006
Say what you want about the SDTS format, however, given that data format there's not much you can do about that. But what about access to native USGS SDTS DEM data? You actually do have a say (somewhat) about it and many GIS professionals are still left wondering why these data are only available from a select few commercial data providers (portals)? Read on as we explore this topic a little deeper.
The USGS maintains an official SDTS discussion list, aptly named the SDTSlist. This community resource is moderated by USGS staff and is used by those seeking information or help with SDTS format GIS data products (like the USGS SDTS DEMs). If you've been listening on the list (like yours truly) you've no doubt heard others pose the question... "why are the SDTS DEMs only available from 3 commercial data outlets". Typically, posting this question will result in some heated exchanges or lively discussions if some of the commercial providers are also listening in ;0) Given that the list is moderated the USGS likely limits the responses to a select and helpful few. If you've ever witnessed this question asked on a general, non-moderated discussion forum or Usenet list you've likely witnessed some very heated discussions.
Recently, a thread on the SDTSlist came through as follows:
I'm very new at mapping so excuse my ignorance if I'm totally off base. I read this about getting SDTS DEM files on the USGS webpage:
1) The original DEM 7.5 minute tiled data available only in Spatial Data Transfer Standard (
And the reasoning for this is:
The decision to provide SDTS DEMs through the GIS Data Depot is consistent with the USGS goal of making more public domain data available at no charge while enabling the private sector to have a greater role in the distribution of USGS data. SDTS DEMs placed on media in response to customer orders will be sold by the GeoCommunity at a price less than the USGS currently charges.
Looking at datadepot, it costs $995 to buy SDTS DEM on CD for the entire USA. You can download it for free but you have to click a million links to do it and they don't allow web spiders to get the data automatically. It'll take months to manually download it all.
Looking at mapmart I can't see any clear way to get it for free.
And looking at ATDI-us you have to select a lat/long, again making it difficult to get the entire data set.
Can we just have a FTP server where we can get the entire lot? These private sector implementations are either very poorly implemented or purposely designed to make it very difficult to get the entire data set.
A USGS representative graciously took some time to provide a detailed response. It read as follows:
We greatly appreciate the comments and suggestions from the members of the list. Many of you have been around longer than me, and I've been a part of the list for about six years now. Your participation and suggestions have been a large part of why the SDTS DEM dataset remains an important and viable dataset. Thank you.
Although going through our commercial venders for SDTS DEMs may not always be the easiest or most efficient method, they do provide the data free of charge. It would have been great if the USGS was able to continue serving these data via USGS ftp site, but unfortunately we were not. Please keep in mind that commercial vendors are in business to make a profit. I, for one, greatly appreciate the time and effort put forth by our three venders, MapMart, GeoCommunity, and ATDI, to continue to offer USGS SDTS DEMs free of charge.
I'm not sure what the going rate is to host and maintain a server with several hundred gigabytes of data, and handling hundreds of thousands of file downloads in addition to providing monthly maintenance, but it must be substantial. [actually, the cost for such bandwidth coupled with applications developed using Open Source solutions are substantially less than now than when these arrangements were first setup so it really isn't that cost prohibitive?]
We welcome other entities to partner with the USGS in serving SDTS DEMs free of charge to the public, but for now, MapMart, GeoCommunity, and ATDI have been the only three to enter into an agreement with the USGS.
About the Data Distribution Agreement
Essentially it boils down to this... the decision to "farm" out the DEM data is an effort to make the data more accessible. Unfortunately many GIS professionals don't feel that the agreement has in fact lived up to the mandate.. so I ask you... Are these data more accessible given they are served up by commercial outlets? I'll concede, the data are [relatively] easy to locate, however, access is another story. The datadepot provides free data via an agonizingly slow server, although users are "encouraged" to buck up and pay for a faster pipe (they call it the "fat pipe"). Free downloads can be had by clicking back and forth in search of required files, the goal here is to fatten up page views and the subsequent banner impressions from advertisers. "Regular" downloads are provided free, however, only to registered site users who have created an account and provided the company with personal information. On the flip side, the data can be written on CD-ROM and delivered via mail. Mapmart encourages users to register and provide personal information, in exchange data is available in blocks of 10 files at a time... no doubt grabbing a county's worth of data will require some patience. Mapmart provides a webmap interface to access data, however, I find it rather confusing as its not that apparent that these data are free since you are required to "order" your data blocks (to me this implies a sale). ATDI provides a really nice interface where users specify coordinates and retrieve the resulting DEM file, however, grabbing a large number of files will require patience and loads of time. So... does this mean the data are accessible? Well, technically, YES. Is it convenient? Hardly.
ATDI, a USGS business partner, makes available a free DEM server where users are prompted to input the lat/long of a desired region.
Mapmart provides users with a webmap interface developed with MapInfo MapXtreme. A user account is required to get "free data"... free? You tell me!
"Before you can download any data from our website, we require that you log in to your Account"
Downloading DEMs from the data depot involves clicking through a series of textual links organized by State, then County. Users must know the quad number of the area of interest in order to obtain data. Furthermore, downloads are open only to registered users - free?
The USGS' Policy
The following is the official policy according to the USGS website... The U.S. Geological Survey (USGS) has entered into an agreement with the GeoCommunity, MapMart.com, and ATDI, to serve updated, SDTS format, Digital Elevation Models (DEMs) through the GIS Data Depot at http://www.gisdatadepot.com and at MapMart.com at http://www.mapmart.com, and ATDI at http://www.atdi-us.com for no charge. The 7.5' SDTS DEM data are also available for purchase via premium (fast) download and on CD-ROM from GeoCommunity and for purchase on CD-ROM from MapMart.com.
The decision to provide SDTS DEMs through commercial vendors is consistent with the USGS goal of making more public domain data available at no charge while enabling the private sector to have a greater role in the distribution of USGS data. SDTS DEMs placed on media in response to customer orders will be sold by our partners at a price less than the USGS currently charges.
The GeoCommunity, MapMart.com, and ATDI will continue to receive SDTS versions of the DEMs as they are made available by the USGS. Native format DEMs are still available for sale from USGS on various media and via ftp. (Source:http://edc.usgs.gov/geodata/)
Fact... SDTS DEM are only "officially" available from the USGS DEM distribution partners. However, what you may not know is that these data are also available from numerous other sources (See State GIS Clearinghouse Directory - Update, July 2004). How so? Simple... given that the data are not subject to a copyright and are in the public domain, users are pretty much free to download, reformat, repost, re-serve, or what have you... as a result, the same DEM files are available via html, FTP, CD-ROM, DVD, and web IMS from countless government, educational, and even commercial GIS web portals. Users should exercise caution when working with data from unofficial sources as the data of these data may differ from the same files available from the official portals. On the upside, if you visit a third party you may often have access to data that have some value added. This is because the source may have already gone to great lengths in reformatting, reprojecting, or translating these data into something that is more suitable for your needs... you know what I mean if you've fought with DEM data in an effort to merge files that are in different projections, different UTM zones, or even different data formats. Look hard enough and you'll find the SDTS DEMs served up in DEM format rather than the painful SDTS data format.
Need a business model?
Taking this idea a bit further, essentially there's nothing preventing any GIS consultant, student, or what have you from downloading, repackaging, and selling State Data bundles from your own website. Granted, you likely won't have the USGS' stamp of approval and you may not have the most current DEM data, however, you'll still be providing a service, you'll still earn a decent buck, and chances are, you'll likely sell the data for a cost much less than what you can get from the "other" sources. On the flip-side, if you locate a State clearinghouse that's serving the most recent data or even selling them, you're likely more than welcome to download of buy the data, repackage them or serve them up from your server... give them away or even sell them. I've consulted several clearinghouse directors and they welcome such a service as they see this as taking the pressure of their servers and saving them the trouble.
Another option... consider the Florida GIS Data Sharing Network (see http://groups.google.com/group/GIS-Data). This popular group brings together GIS professionals willing to share their data... what great idea! Think about it... you download or buy some DRGs, DEMs, DOQs, parcel data, or what have you. USing the list you can easily arrange to swap, share, exchange, or give away your GIS data needed by other professionals for their projects. To date the project appears to have been quite succesful and I'm actually quite surprised that other such cooperatives haven't popped up (if so, please tell me about it). For other data sharing cooperatives see http://www.gis-data.blogspot.com/ & a good example from Palm Beach County.
Online resources like this one in Washington State serve up 30m DEMs using a simple image map for quick retrieval of ZIP compressed DEMs - they also havbe 10m DEMS. Such resources are plentiful and easily found for pretty much every State.
Users should also consult the Seamless data distribution system at http://seamless.usgs.gov where you can access the National Elevation Dataset (NED), in particular, the 1/3 arcscond data coverage. NED 1/3 arc second (~ 10 meter resolution) is processed and assembled the same as the NED 1 arc second, but the source data is 10 meter elevation data or higher resolution. Of interest, The coverage area is approximately 70% of the United States. There are 1/9 arcsecond data, however, the coverage is minimal. NED 1/9 arc second (~ 3 meter resolution)is processed and assembled the same as the NED 1 and 1/3 arc second, but the source data is using mostly LIDAR elevation data sources. Of note, the NED is derived from USGS DEM data.
Finally, another source that you absolutely MUST consult is the USDA Geospatial Gateway - home to NAIP ortho photography, DEMs, and a "whackin pant-load" of other spatial datasets - See http://datagateway.nrcs.usda.gov/GatewayHome.html
Conclusion
The USGS' policy to make SDTS DEMs accessible falls short... there's little doubt about that. On the upside, the user community has picked up the ball and as a result there are many choices available to users. Hats off to State Clearinghouses, GIS departments from all level of government, EDUs, developers, and even some commercial data providers that contributed and helped make USGS DEMs accessible.
So what's your opionion? Are DEMS and other USGS data products accessible? Are you satisfied? Can you easily find affordable data for use in your projects? I welcome your comments.
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Say what you want about the SDTS format, however, given that data format there's not much you can do about that. But what about access to native USGS SDTS DEM data? You actually do have a say (somewhat) about it and many GIS professionals are still left wondering why these data are only available from a select few commercial data providers (portals)? Read on as we explore this topic a little deeper.
