In the past I have written about the USGS Seamless Server web site as a source of SRTM Digital Elevation Models. The USGS Seamless Server is also a very rich website archiving high-resolution color aerial ortho imagery for all of the United States. The Seamless Server seems to archive all of the data that is available for a given area. Some areas (like New York State for example) are more extensively covered than others. The whole of the USA seems to be at least covered by the National Agricultural Imagery Program (NAIP) data set. The United States Farm Service Agency (FSA) runs the NAIP, which in turn is a part of the United States Department of Agriculture. According to the FSA Website , the National Agriculture Imagery Program (NAIP) acquires aerial imagery during the agricultural growing seasons in the continental U.S. The resolution is 1m and the images usually contain 3 visible spectrum bands (blue, green and red). Some of the imagery contains a fourth near infrared (NIR) band. A primary goal of the NAIP program is to make digital ortho photography available to governmental agencies and the public within a year of acquisition. All of the data acquired to-date has been from aircraft over flights. Although the NAIP specification allows satellite imagery to be used, none has been yet.

NAIP coverage for all of the USA seems to be complete, although that coverage may not all be acquired during the same year, and not all of the data is available from the Seamless Server. Although this is an agricultural service, the FSA will assist states that wish to extend coverage from strictly agricultural areas to the entire state. As a result, New York State's urban areas such as Manhattan and Long Island are included in that state's coverage. Few states receive coverage every year, however over a ten-year period the entire continental United States receives coverage at least once and many states receive coverage periodically during several years.

The data is presented in a format that is ideal for cartographers. File format is GeoTiff; so extensive metadata is embedded in the file. The image tiles correspond to USGS Quarter Quads, so they have N/S alignment consistent with USGS topographic maps and other cartographic data. And they are orthorectified so that apparent inaccuracies due to terrain variation have been removed. A complete data description is given in the NAIP Information Sheet

Usage restrictions appear to be minimal. The FSA website states:

"Most information presented on the FSA Web site is considered public domain information. Public domain information may be freely distributed or copied, but use of appropriate byline/photo/image credits is requested. Attribution may be cited as follows: "U. S. Department of Agriculture, Farm Service Agency."

"Some materials on the FSA Web site are protected by copyright, trademark, or patent, and/or are provided for personal use only. Such materials are used by FSA with permission, and FSA has made every attempt to identify and clearly label them. You may need to obtain permission from the copyright, trademark, or patent holder to acquire, use, reproduce, or distribute these materials."

There are few down sides for this data. One obvious shortcoming is lack of complete NIR band coverage. It seems odd that an agricultural agency would fund expensive aerial photography without acquiring infrared coverage. A second minor drawback for some may be the leaf-on nature of the imagery as this hides ground features in forested areas. However, many users will see this as a plus as the foliage in full leaf is certainly pleasing to look at. Another drawback is the akward Seamless Server user interface. The USGS Seamless Server is extremely slow for even simple operations like panning and zooming the map. The coverage and selection map itself is about the size of four postage stamps while the majority of the page is occupied by the coverage keys, the navigation keys, or nothing. The navigation tools are OK but response for all is slow. Once you have sort of zeroed in you can download by coordinates, which is helpful. Probably the most annoying thing about the experience is that the Server page is not synchronized with the Request Summary page. As a result, regardless of the coverage that you select on the Server page, the Request Summary page always defaults to National Elevation Dataset (NED) coverage. You have to "Modify Data Request" to select what you want, which is slow. Often the amount of requested data will exceed the Request page limit, which requires you to submit another request... you get the picture.

These are mostly gripes however. The data itself is excellent and best of all zero-cost (at least for that offered on the USGS Seamless Server). While most countries of the world do not offer any free geospatial or remotely-sensed data to their citizens or anyone else, the USA offers essentially complete coverage of its country at 1m resolution to anyone who queries its server. This data, along with associated DEM and DRG topographic map data provides extremely useful and valuable information for a wide variety of uses.

I provided a few examples of the imagery for various parts of the USA to the right.