15.1 What Other Kinds of Geospatial Data Are Available Online?

The previous chapters have described numerous datasets and how to obtain them (either for free or for minimal cost), often through the applications in the chapters. If you want to build a database of available geospatial data, you could get your hands on:

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National Map an online basemap of downloadable geospatial data maintained and operated by the USGS and part of the National Geospatial Program

Beyond these options, there are plenty of other online resources for geospatial data, and most of them are free. State, county, or municipal Web services will often make their GIS data and remotely sensed imagery easily accessible, available, and totally free of charge (as we saw in Chapter 5). At the national level, the USGS maintains a large geospatial data distribution program called the National Map. Users of the National Map can access multiple types of datasets, including National Elevation Data (NED), hydrography, transportation, land-cover data, boundary files, and many more—in formats that GIS software can read. The National Map is just one part of the larger coordinated vision that comprises the National Geospatial Program, and it serves as a source of geospatial data for the United States (see Figure 15.1 and Hands-on Application 15.2: The National Map Viewer for more information about the National Map). You can think of the National Map as a “one-stop-shopping” venue for free geospatial data—numerous types of datasets are available for a geographic area that you define, a very useful option that prevents you from having to find and download data from multiple sources, then clip or alter the data to make it fit together in a way that will provide the information you want about the region you’re examining. If you’re studying East Liverpool, Ohio, you can use the National Map to download land-cover data, national elevation (NED) data, boundary files, water features, and transportation layers of only the East Liverpool area.

FIGURE 15.1 The online National Map Viewer.(Source: U.S. Geological Survey)

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!geo! HANDS-ON APPLICATION 15.2

The National Map Viewer

You can access the National Map online at http://nationalmap.gov/index.html. Select the option for the National Map Viewer and Download Platform. From this new page, choose the option to go to the Viewer. A new Web page will open with the Viewer itself, the tool for accessing data via the National Map. The National Map can be used to view available data—from the Overlays options on the left side of map, you can select what layers to display. High-resolution imagery can be accessed as an additional visible layer from the Imagery option on the right side of the map.

The layers you’re viewing in the National Map can also be downloaded for use in GIS or other software programs. First, search for an area of interest (go to Reno, Nevada). Zoom in to this area, and when the view of the map changes, press the Download Data button in the upper-right corner of the map. New download options will appear that allow you to select the extent of the area you want to download data for. Next, the data layers that are available for download will be shown (these will include US Topo, structures, transportation, boundaries, hydrography, land cover, elevation, and orthoimagery) as well as the data formats these layers are available in. Select the layers you want, choose Add to Cart, and then follow the steps to download your data (you will have to register with the USGS—at the time of writing, they will send you an e-mail with a link you can use to retrieve your data).

Expansion Questions:

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SDTS the Spatial Data Transfer Standard, a “neutral” file format for geospatial data, which makes the data capable of being imported into various geospatial software programs

Sometimes geospatial data comes available in a format called SDTS (the Spatial Data Transfer Standard), a system established by the United States government. The intent with SDTS was to deliver data in a file format that’s “neutral,” rather than software-specific. Agencies like the USGS, NOAA, and the Census Bureau sometime utilize SDTS as the format for delivering their geospatial data to you. Software programs often have a converter that enables the import of data in SDTS format to a form directly readable by the software (for instance, ArcGIS has a utility to import an SDTS DLG into a coverage format that you can use).

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cloud a computer structure wherein a user’s data, resources, or applications are kept at another location and made available to the user over the Internet

Online resources are the quickest and easiest way to access geospatial data. Whether you want to acquire archived satellite imagery or get the newest updates for Google Earth, you can do everything via the Internet. The same holds true with distributing your own data and information—setting up a Web interface where your data can be accessed interactively is the way to go. Geospatial technology is increasingly becoming part of a field referred to as the cloud, wherein resources (such as data storage) are being utilized at another location but served to a user across the Internet. The cloud is structured to let you store your data in available space on other servers at other locations, but in a way that allows you to access it when you need via the Internet. Similarly, other people would be able to access your data through these other servers that it resides on. However, there’s much more to the cloud than simply serving datasets to users, as the cloud structure can be used for a wide variety of geospatial applications.