After a bit of a delay, I have finally migrated all of the USDA-NCSS digital soil survey (AZ, CA, NV), 2005se Tiger, and other misc. data from shapefile format to a PostGIS database. In doing so, seamless access to the entire set of detailed (SSURGO) and generalized (STATSGO) polygon data is now possible through our online soil survey. At the Map unit level, links to adjacent soil polygons, along with a local area calculation are just some of the new possibilities of a spatially-enabled database (PostGIS). Note that DOQQ data is not locally stored for AZ and NV. Clicking on the "print" icon in the map interface at scale of < 1:7000 will fetch DOQQ data from Terraserver in these areas. Also the LandSat mosaic for AZ needs to be re-done with i.landsat.rgb, found in GRASS6.1-CVS. A quick comparison of LandSat channel blending is here. Subsequent changes will include thematic mapping of soil properties and visualizations of difference in soil properties across scales. See a simple summary, in case-study format on the PostGIS website. Thanks to Paul Ramsey for doing the write-up.

Fig 1: map interface

Fig 2: UMN Mapserver Application

Fig 3: STATSGO polygon detail

Fig 4: SSURGO polygons

Fig 5: SSURGO polygon detail

Fig 6: soil data summary

Fig 7: land suitability ratings

 
Background
Nearly 2 years have elapsed since we put together an online soil survey for AZ, CA, and NV, based entirely on open source tools. GDAL and GRASS were used to pre-process spatial data, MySQL and PostGIS are used to store spatial and attribute data, UMN Mapserver is used to render map images, and PHP-Apache is used to glue it all together. Our first public prototype was advertised just as the USDA-NRCS announced their Web Soil Survey. We often advise parties interested in soils data to use both methods of accessing soil survey information, as each has its respective strong points. Our goal is to provide people a simple means of quickly accessing specific soil properties, with inline definitions to specialized terminology and interpretations. Several methods exists for locating soil data at a given location:

• clickable map (Fig 1)
• street address
• CA zip code
• latitude longitude from NAD83/WGS84 datum
• CA PLSS Township, Range, Section, and Section fractions

 
Example Session
Figures 2 through 7 represent an example session of interactively panning, zoooming, and eventially querying a SSURGO polygon near Fresno, Ca. An AJAX-style UMN Mapserver application was created, based on the excellent dBox sample code provided by the Mapserver team. Once a user has located a soil polygon of interest (SSURGO or STATSGO), attributes associated with this polygon can be queried with the "info" tool . At this point, depending on the scale, the user is presented with a list of soil types (components) found within the queried polygon (SSURGO example). Clicking on of these links brings up a page on that specific soil type (Figs 6 and 7). Graphical summaries of key soil physical and chemical properties assist with quick recognition of key diagnostic features (sample page). A break-down of the US Soil Taxonomy terminology serves as an educational tool for interested parties. Links to outside sources of relevant data are automatically constructed and included in this summary as well:

• USDA-NRCS Offical Soil Series Descriptions
• USDA-NCSS Pedon Laboratory Data
• Nitrate Groundwater Contamination Index
• definitions of terms and interpretations from the Soil Survey Handbook

 
Finally, our online soil survey, Soil Web, will be used as the foundation for a new educational website on the soils of Pinnacles National Monument, CA. Details on this project can be found on this page.