Soil Survey Geographic (SSURGO) database for Napa County, California

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Frequently anticipated questions:


What does this data set describe?

Title:
Soil Survey Geographic (SSURGO) database for Napa County, California
Abstract:
This data set is a digital soil survey and generally is the most detailed level of soil geographic data developed by the National Cooperative Soil Survey. The information was prepared by digitizing maps, by compiling information onto a planimetric correct base and digitizing, or by revising digitized maps using remotely sensed and other information. This data set consists of georeferenced digital map data and computerized attribute data. The map data are in a 7.5 minute quadrangle format and include a detailed, field verified inventory of soils and nonsoil areas that normally occur in a repeatable pattern on the landscape and that can be cartographically shown at the scale mapped. A special soil features layer (point and line features) is optional. This layer displays the location of features too small to delineate at the mapping scale, but they are large enough and contrasting enough to significantly influence use and management. The soil map units are linked to attributes in the National Soil Information System relational database, which gives the proportionate extent of the component soils and their properties.
Supplemental_Information:
Digital versions of hydrography, cultural features, and other associated layers that are not part of the SSURGO data set may be available from the primary organization listed in the Point of Contact.
  1. How should this data set be cited?

    U.S. Department of Agriculture, Natural Resources Conservation Service, 20030624, Soil Survey Geographic (SSURGO) database for Napa County, California: U.S. Department of Agriculture, Natural Resources Conservation Service, Fort Worth, Texas.

    Online Links:

    Other_Citation_Details: ca055

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -122.750
    East_Bounding_Coordinate: -122.000
    North_Bounding_Coordinate: 38.875
    South_Bounding_Coordinate: 38.125

  3. What does it look like?

  4. Does the data set describe conditions during a particular time period?

    Beginning_Date: 03-Feb-1999
    Ending_Date: 24-Jun-2003
    Currentness_Reference: publication date

  5. What is the general form of this data set?

  6. How does the data set represent geographic features?

    1. How are geographic features stored in the data set?

      This is a Vector data set.

    2. What coordinate system is used to represent geographic features?

      Grid_Coordinate_System_Name: Universal Transverse Mercator
      Universal_Transverse_Mercator:
      UTM_Zone_Number: 10
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.9996
      Longitude_of_Central_Meridian: -123.0
      Latitude_of_Projection_Origin: 0.0
      False_Easting: 500000
      False_Northing: 0.0

      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 1.8288
      Ordinates (y-coordinates) are specified to the nearest 1.8288
      Planar coordinates are specified in meters

      The horizontal datum used is North American Datum of 1983.
      The ellipsoid used is Geodetic Reference System 80.
      The semi-major axis of the ellipsoid used is 6378137.0.
      The flattening of the ellipsoid used is 1/298.257.

  7. How does the data set describe geographic features?

    Special Soil Features
    Special Soil Features represent soil, nonsoil, or landform features that are too small to be digitized as soil delineations (area features). (Source: U.S. Department of Agriculture. 1993. Soil Survey Manual. Soil Surv. Staff, U.S. Dep. Agric. Handb. 18.)

    Special Soil Features Codes
    Special Soil Features Codes represent specific Special Soil Features. These features are identified with a major code, a minor code, and a descriptive label. The codes and label are assigned to the point or line assigned to represent the feature on published maps. (Source: U.S. Department of Agriculture. 1993. Soil Survey Manual. Soil Surv. Staff, U.S. Dep. Agric. Handb. 18; U.S. Department of Agriculture. (current issue). National Soil Survey Handbook, title 430-VI, part 647. Soil Conserv. Serv.)

    Formal codeset
    Codeset Name:Classification and Correlation of the Soils of Napa County, California
    Codeset Source:U.S. Department of Agriculture, Natural Resources Conservation Service

    Entity_and_Attribute_Overview:
    Map Unit Delineations are closed polygons that may be dominated by a single soil or nonsoil component plus allowable similar or dissimilar soils, or they can be geographic mixtures of groups of soils or soils and nonsoil areas. The map unit symbol uniquely identifies each closed delineation map unit. Each symbol is linked to a map unit name. The map unit symbol is also the key for linking information in the National Soil Information System tables. The map unit symbols are not carried within the modified Digital Line Graph file; however, they are made available in a companion attribute file. The attribute file links the minor codes in the Digital Line Graph files to the map unit symbols.
    Map Unit Delineations are described by the National Soil Information System database. This attribute database gives the proportionate extent of the component soils and the properties for each soil. The database contains both estimated and measured data on the physical and chemical soil properties and soil interpretations for engineering, water management, recreation, agronomic, woodland, range, and wildlife uses of the soil.
    The National Soil Information System database contains static metadata. It documents the data structure and includes such information as what tables, columns, indexes, and relationships are defined as well as a variety of attributes of each of these database objects. Attributes include table and column descriptions and detailed domain information.
    The National Soil Information System database also contains a distribution metadata. It records the criteria used for selecting map units and components for inclusion in the set of distributed data.
    Special features are described in the feature table. It includes a feature label, feature name, and feature description for each special and ad hoc feature in the survey area.
    Entity_and_Attribute_Detail_Citation:
    U.S. Department of Agriculture. 1999. Soil Taxonomy: A basic system of soil classification for making and interpreting soil surveys. Soil Conserv. Serv., U.S. Dep. Agric. Handb. 436. U.S. Department of Agriculture. (current issue). Keys to Soil Taxonomy. Soil Surv. Staff, Soil Conserv. Serv. U.S. Department of Agriculture. (current issue). National Soil Survey Handbook, title 430-VI. Soil Surv. Staff, Natural Resources Conservation Service. U.S. Department of Agriculture. 1993. Soil Survey Manual. Soil Surv. Staff, U.S. Dep. Agric. Handb. 18.


Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)

  2. Who also contributed to the data set?

  3. To whom should users address questions about the data?

    U.S. Department of Agriculture, Natural Resources Conservation Service
    State Soil Scientist
    430 G Street #4164
    Davis, California 95616-4164

    530 792 5640 (voice)
    530 792 5794 (FAX)


Why was the data set created?

SSURGO depicts information about the kinds and distribution of soils on the landscape. The soil map and data used in the SSURGO product were prepared by soil scientists as part of the National Cooperative Soil Survey.


How was the data set created?

  1. From what previous works were the data drawn?

    NRCS1 (source 1 of 8)
    U.S. Department of Agriculture, Soil Conservation Service, 1978, Soil Survey of Napa County, California: Government Printing Office, Washington, D.C..

    Type_of_Source_Media: paper
    Source_Scale_Denominator: 24000
    Source_Contribution: source used as reference of soils and landscapes

    NRCS2 (source 2 of 8)
    U.S. Department of Agriculture, Natural Resources Conservation Service, unpublished material, publication negatives.

    Type_of_Source_Media: stable-base material
    Source_Scale_Denominator: 24000
    Source_Contribution: source used to make publication positives

    NRCS3 (source 3 of 8)
    U.S. Department of Agriculture, Natural Resources Conservation Service, unpublished material, publication positives.

    Type_of_Source_Media: stable-base material
    Source_Scale_Denominator: 24000
    Source_Contribution:
    scan source containing soil lines and special soil features, and cultural features

    USGS1 (source 4 of 8)
    U.S. Geological Survey, 1954, multiple 7.5 minute topographic quadrangles.

    Type_of_Source_Media: stable-base material
    Source_Scale_Denominator: 24000
    Source_Contribution: source material used to digitize county boundaries

    NRCS4 (source 5 of 8)
    U.S. Department of Agriculture, Natural Resources Conservation Service, unpublished material, DLG-3 files.

    Type_of_Source_Media: magnetic tape
    Source_Scale_Denominator: 24000
    Source_Contribution:
    digitized soil and special soil feature layers for evaluation for SSURGO

    NRCS5 (source 6 of 8)
    U.S. Department of Agriculture, Natural Resources Conservation Service, 1999, Soil Survey Geographic (SSURGO) database for Napa County, California: U.S. Department of Agriculture, Natural Resources Conservation Service National Cartography and Geospatial Center, Ft. Worth, Texas.

    Type_of_Source_Media: online
    Source_Scale_Denominator: 24000
    Source_Contribution: source used for digital revision

    NRCS6 (source 7 of 8)
    U.S. Department of Agriculture, Natural Resources Conservation Service, unpublished material, ARC EXCHANGE files for the soil survey of Napa County, California.

    Type_of_Source_Media: CD-ROM
    Source_Scale_Denominator: 24000
    Source_Contribution: source used for evaluation for SSURGO

    NRCS7 (source 8 of 8)
    U.S. Department of Agriculture, Natural Resources Conservation Service, unpublished material, MrSID compressed image for Napa County, California.

    Type_of_Source_Media: CD-ROM
    Source_Scale_Denominator: 24000
    Source_Contribution: NAD83 compilation base

  2. How were the data generated, processed, and modified?

    Date: 1998 (process 1 of 7)
    Napa County, California had a previously published soil survey, 1978 at a scale of 1:24000. An evaluation was made of the survey in 1998. It was determined that the soil map unit delineations and map unit components were accurate.

    Data sources used in this process:

    • NRCS1

    Date: 1998 (process 2 of 7)
    The publication negatives were used to make the publication positives and contained soil line delineations, labels and special and cultural features. The publication positives were raster scanned on an Anatek Eagle 4050 scanner at 300 DPI at Midwest Graphics in Milwaukee, WI. The processing, raster editing, map neatline development, labeling, edge matching, vector conversion and editing of the soils were done in LT4X, Version 4.11 software. Edits on labeling and line delineations were performed by soil scientists on staff at the Natural Resources Conservation Service, State Office in Davis, California. The soil scientists' edits were applied in LT4X software and initial quality checks of soil line delineations, labeling, and edgematching were accomplished according to SSURGO specifications. The county boundaries were digitized from the 7.5 minute topographic quadrangles. The special soil features were manually digitized from the scan source. The data were created and maintained in North American Datum of 1927 by cartographic technicians on staff at the Montana Digitizing Unit in Bozeman. Digital Line Graph, Optional (DLG-3) files were written with export_area SSURGO and export_spec SSURGO options in LT4X, Version 4.11.

    Data sources used in this process:

    • NRCS1, NRCS2, NRCS3, USGS1

    Date: 1999 (process 3 of 7)
    The DLG-3 files were imported for verification in ARC/INFO, Version 7.0.4 by cartographic technicians on staff at the Montana Digitizing Unit in Bozeman. ARCEDIT was used to correct extra vertices, pseudo nodes, and label mismatches to establish an exact join to quadrangles within the survey area. New DLG-3 files were written. The DLG-3 files were forwarded to the National Cartography and Geospatial Center in Ft. Worth, Texas for archiving and distribution.

    Data sources used in this process:

    • NRCS1, NRCS4

    Date: 1998 (process 4 of 7)
    The Map Unit Interpretations Record data base was developed by the Natural Resources Conservation Service soil scientist according to national standards.

    Data sources used in this process:

    • NRCS1

    Date: 2003 (process 5 of 7)
    The National Soil Information System data base was developed by the Natural Resources Conservation Service soil scientists according to national standards.

    Data sources used in this process:

    • NRCS1

    Date: 2003 (process 6 of 7)
    County-wide coverages of the 1999 SSURGO data for area and special features were imported to ARCMAP 8.0 by soil scientists at the Natural Resources Conservation Service State Office in Davis, California. The coverages were projected to North American Datum of 1983. EDIT TOOLS were used to adjust soil delineations along riparian areas, and water areas in order to fit current imagery. The data were exported to ARC EXCHANGE files and were delivered to certification staff at the Montana Digitizing Unit for evaluation.

    Data sources used in this process:

    • NRCS5, NRCS6, NRCS7

    Date: 2003 (process 7 of 7)
    The ARC EXCHANGE files were imported to ARC/INFO 8.1 by cartographic technicians on staff at the Montana Digitizing Unit. NAD83, 7.5 minute quadrangle grid was used to intersect the county wide SHAPE files. Quadrangles were then reselected for the Napa County survey area. Quality control routines were completed on all quadrangles for area and special feature coverages. ARCEDIT was used to correct label errors and node mismatches. Digital Line Graph Optional, (DLG-3) files were written. The DLG-3 files were imported to ARC/INFO 8.0 and processed through revised evaluation program macros dated October 1998. New DLG-3 files were written. The data were forwarded to the National Cartography and Geospatial Center in Ft. Worth, Texas for archiving and distribution.

    Data sources used in this process:

    • NRCS5, NRCD6

  3. What similar or related data should the user be aware of?

    U.S. Department of Agriculture, Soil Conservation Service, 1978, Soil Survey of Napa County, California.

    Other_Citation_Details:
    This soil survey contains information that can be applied in managing farms and wetlands; in selecting sites for roads, ponds, buildings, and other structures; and in judging the suitability of tracts of land for farming, industry, and recreation. This soil survey depicts information about the kinds and distribution of soils on the landscape. The soil map and data used in the SSURGO product were prepared by soil scientists as part of the National Cooperative Soil Survey.


How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?

    Attribute accuracy is tested by manual comparison of the source with hard copy plots and/or symbolized display of the map data on an interactive computer graphic system. Selected attributes that cannot be visually verified on plots or on screen are interactively queried and verified on screen. In addition, the attributes are tested against a master set of valid attributes. All attribute data conform to the attribute codes in the signed classification and correlation document and amendment(s).

  2. How accurate are the geographic locations?

    The accuracy of these digital data is based upon their compilation to base maps that meet National Map Accuracy Standards. The difference in positional accuracy between the soil boundaries and special soil features locations in the field and their digitized map locations is unknown. The locational accuracy of soil delineations on the ground varies with the transition between map units. For example, on long gently sloping landscapes the transition occurs gradually over many feet. Where landscapes change abruptly from steep to level, the transition will be very narrow. Soil delineation boundaries and special soil features generally were digitized within 0.01 inch of their locations on the digitizing source. The digital map elements are edge matched between data sets. The data along each quadrangle edge are matched against the data for the adjacent quadrangle. Edge locations generally do not deviate from centerline to centerline by more than 0.01 inch.

  3. How accurate are the heights or depths?

  4. Where are the gaps in the data? What is missing?

    A map unit is a collection of areas defined and named the same in terms of their soil and/or nonsoil areas. Each map unit differs in some respect from all others in a survey area and is uniquely identified. Each individual area is a delineation. Each map unit consists of one or more components. Soil scientists identify small areas of soils or miscellaneous (nonsoil) areas that have properties and behavior significantly different than the named soils in the surrounding map unit. These minor components may be indicated as special features. If they have a minimal effect on use and management, or could not be precisely located, they may not be indicated on the map.
    Specific National Cooperative Soil Survey standards and procedures were used in the classification of soils, design and name of map units, and location of special soil features. These standards are outlined in Agricultural Handbook 18, Soil Survey Manual, 1993, USDA, SCS; Agricultural Handbook 436, Soil Taxonomy, Soil Survey Staff, 1975, USDA, SCS; and all Amendments; Keys to Soil Taxonomy, Soil Survey Staff, (current issue); National Soil Survey Handbook, title 430-VI, (current issue).
    The actual composition and interpretive purity of the map unit delineations were based on data collected by scientists during the course of preparing the soil maps. Adherence to National Cooperative Soil Survey standards and procedures is based on peer review, quality control, and quality assurance. Quality control is outlined in the memorandum of understanding for the soil survey area and in documents that reside with the Natural Resources Conservation Service state soil scientist. Four kinds of map units are used in soil surveys: consociations, complexes, associations, and undifferentiated groups.
    Consociations - Consociations are named for the dominant soil. In a consociation, delineated areas are dominated by a single soil taxon and similar soils. At least one half of the pedons in each delineation are of the same soil component so similar to the named soil that major interpretations are not affected significantly. The total amount of dissimilar inclusions of other components in a map unit generally does not exceed about 15 percent if limiting and 25 percent if nonlimiting. A single component of a dissimilar limiting inclusion generally does not exceed 10 percent if very contrasting.
    Complexes and associations - Complexes and associations are named for two or more dissimilar components with the dominant component listed first. They occur in a regularly repeating pattern. The major components of a complex cannot be mapped separately at a scale of about 1:24,000. The major components of an association can be separated at a scale of about 1:24,000. In each delineation of either a complex or an association, each major component is normally present, though their proportions may vary appreciably from one delineation to another. The total amount of inclusions in a map unit that are dissimilar to any of the major components does not exceed 15 percent if limiting and 25 percent if nonlimiting. A single kind of dissimilar limiting inclusion usually does not exceed 10 percent.
    Undifferentiated groups - Undifferentiated groups consist of two or more components that do not always occur together in the same delineation, but are included in the same named map unit because use and management are the same or similar for common uses. Every delineation has at least one of the major components and some may have all of them. The same principles regarding proportion of inclusions apply to undifferentiated groups as to consociations.
    Minimum documentation consists of three complete soil profile descriptions that are collected for each soil added to the legend, one additional per 3,000 acres mapped; three 10 observation transects for each map unit, one additional 10 point transect per 3,000 acres.
    A defined standard or level of confidence in the interpretive purity of the map unit delineations is attained by adjusting the kind and intensity of field investigations. Field investigations and data collection are carried out in sufficient detail to name map units and to identify accurately and consistently areas of about 6 acres.

  5. How consistent are the relationships among the observations, including topology?

    Certain node/geometry and topology GT- polygon/chain relationships are collected or generated to satisfy topological requirements (the GT-polygon corresponds to the soil delineation). Some of these requirements include: chains must begin and end at nodes, chains must connect to each other at nodes, chains do not extend through nodes, left and right GT-polygons are defined for each chain element and are consistent throughout, and the chains representing the limits of the file (neatline) are free of gaps. The tests of logical consistency are performed using vendor software. The neatline is generated by connecting the explicitly entered four corners of the digital file. All data outside the enclosed region are ignored and all data crossing these geographically straight lines are clipped at the neatline. Data within a specified tolerance of the neatline are snapped to the neatline. Neatline straightening aligns the digitized edges of the digital data with the generated neatline (i.e., with the longitude/latitude lines in geographic coordinates). All internal polygons are tested for closure with vendor software and are checked on hard copy plots. All data are checked for common soil lines (i.e., adjacent polygons with the same label). Quadrangles are edge matched within the soil survey area and edge locations generally do not deviate from centerline to centerline by more than 0.01 inch. Quadrangles in this survey are joined to quadrangles in the Lake County, the Yolo County, the Solano County, and the Sonoma County, California soil survey areas.


How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?

Access_Constraints: None
Use_Constraints:
The U.S. Department of Agriculture, Natural Resources Conservation Service, should be acknowledged as the data source in products derived from these data. This data set is not designed for use as a primary regulatory tool in permitting or citing decisions, but may be used as a reference source. This is public information and may be interpreted by organizations, agencies, units of government, or others based on needs; however, they are responsible for the appropriate application. Federal, State, or local regulatory bodies are not to reassign to the Natural Resources Conservation Service any authority for the decisions that they make. The Natural Resources Conservation Service will not perform any evaluations of these maps for purposes related solely to State or local regulatory programs.
Photographic or digital enlargement of these maps to scales greater than at which they were originally mapped can cause misinterpretation of the data. If enlarged, maps do not show the small areas of contrasting soils that could have been shown at a larger scale. The depicted soil boundaries, interpretations, and analysis derived from them do not eliminate the need for onsite sampling, testing, and detailed study of specific sites for intensive uses. Thus, these data and their interpretations are intended for planning purposes only. Digital data files are periodically updated. Files are dated, and users are responsible for obtaining the latest version of the data.

  1. Who distributes the data set? (Distributor 1 of 1)

    U.S. Department of Agriculture, Natural Resources Conservation Service, National Cartography and Geospatial Center
    P.O. Box 6567
    Fort Worth, Texas 76115

    800 672 5559 (voice)
    817 509 3469 (FAX)

  2. What's the catalog number I need to order this data set?

    Napa County, California SSURGO

  3. What legal disclaimers am I supposed to read?

    Although these data have been processed successfully on a computer system at the U.S. Department of Agriculture, no warranty expressed or implied is made by the Agency regarding the utility of the data on any other system, nor shall the act of distribution constitute any such warranty. The U.S. Department of Agriculture will warrant the delivery of this product in computer readable format, and will offer appropriate adjustment of credit when the product is determined unreadable by correctly adjusted computer input peripherals, or when the physical medium is delivered in damaged condition. Request for adjustment of credit must be made within 90 days from the date of this shipment from the ordering site. The U.S. Department of Agriculture, nor any of its agencies are liable for misuse of the data, for damage, for transmission of viruses, or for computer contamination through the distribution of these data sets. The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, sex, religion, age, disability, political beliefs, sexual orientation, or marital or family status. (Not all prohibited bases apply to all programs.)

  4. How can I download or order the data?


Who wrote the metadata?

Dates:
Last modified: 24-Jun-2003
Metadata author:
U.S. Department of Agriculture, Natural Resources Conservation Service
State Soil Scientist
430 G Street #4164
Davis, California 95616-4164

530 792 5640 (voice)
530 792 5794 (FAX)

Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)


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