/SSURGO README.TXT Soil Survey Geographic (SSURGO) Data USDA - Natural Resources Conservation Service Comments and Sugestions ======================= We hope that you find this information useful. We would appreciate any comments or suggestions that you may have. Comments or suggestions concerning format and distribution may be directed to the following address. National Cartography and Geospatial Center U.S. Department of Agriculture Natural Resources Conservation Service P.O. Box 6567 Fort Worth, Texas 76115 (800) 672-5559 Telephone (Ordering Information) (402) 437-5423 Telephone (Tech Support) (817) 334-5469 FAX Introduction ============ The map extent for a Soil Survey Geographic (SSURGO) data set is a soil survey area, which may consist of a county, multiple counties, or parts of multiple counties. A SSURGO data set consists of map data, attribute data, and metadata. SSURGO map data are available in modified Digital Line Graph (DLG-3) optional and Arc interchange file formats. Attribute data are distributed in ASCII format with DLG-3 map files and in Arc interchange format with Arc interchange map files. Metadata are in ASCII format. Data Formats ============ DLG-3 ----- The modified Digital Line Graph (DLG-3) file contains header records and data records consisting of node identification records, area identification records, and line identification records. Node records are not attributed with major and minor code pairs. For soil features, the major and minor code pairs are on the area records. For special soil features, the major and minor code pairs are on the line records, except for the lines making up the quadrangle boundary. Each data record is 80 bytes in length and ends with a return character. Map unit symbols are not carried within the modified DLG-3 file; however, they are made available in a companion attribute file. The attribute file links the minor codes in the DLG-3 file to the map unit symbols. Similar map unit symbols in the data set have the same minor code. The data are distributed in a quadrangle format. There is a soil polygon Digital Line Graph file and a companion attribute file for each quadrangle in the soil survey area. If special soil features were mapped, there is also a special soil point and line DLG-3 file and a companion attribute file. These files are available in DOS and UNIX file formats. Coordinate Reference DLG-3 coordinates are in UTM meters. If the horizontal reference of the digitizing source was the North American Datum of 1927, map data referenced to the North American Datum of 1927 are available in the dlg27 directory. Map data shifted to the North American Datum of 1983 are available in the dlg83 directory. If the horizontal reference of the digitizing source was the North American Datum of 1983, map data referenced to the North American Datum of 1927 are not available. File Naming Convention The file naming convention for SSURGO DLG-3 and attribute files follow the data set naming convention used in the USGS National Digital Cartographic Data Base, but with some modifications. A brief description of the naming convention follows: Sample File Name: tyyxxxzz.qft t - indicates type of data (s = SSURGO) yy - indicates southeast latitude of the one-degree block in which the quadrangle resides xxx - indicates southeast longitude of the one-degree block in which the quadrangle resides zz - is the 7.5-minute section number of the one- degree block in which the quadrangle resides (reading left to right from northwest corner) .q - indicates the 3.75-minute quarter of the 7.5- minute quadrangle expressed as an integer (7.5-minute quadrangles are coded as "0") NE - 1 NW - 2 SW - 3 SE - 4 ft - indicates data type af - soil polygon DLG-3 file aa - soil polygon attribute file sf - special soil point and line DLG-3 file sa - special soil point and line attribute file Example 1: Quarter-quadrangle s4309101.2af - a soil polygon DLG-3 file, for the northwest 3.75-minute quarter of the first 7.5-minute quadrangle of the one-degree block, whose southeast corner is 43-degrees north latitude and 91-degrees west longitude. Example 2: Full Quadrangle s4309125.0aa - a soil polygon attribute file, for the 7.5-minute quadrangle whose southeast corner is 30 minutes and 00 seconds north latitude and 52 minutes and 30 seconds west longitude of the one-degree block, whose southeast corner is 43-degrees north latitude and 91-degrees west longitude. Figure 1: One-degree Block Example 1 ----------------------------------------- 44d 00m 00s --------->| 01 | 02 | 03 | 04 | 05 | 06 | 07 | 08 | |----+----+----+----+----+----+----+----| 52m 30s | 09 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | |----+----+----+----+----+----+----+----| 45m 00s | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | |----+----+----+----+----+----+----+----| 37m 30s Example 2 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | --------->|----+----+----+----+----+----+----+----| 30m 00s | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | |----+----+----+----+----+----+----+----| 22m 30s | 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48 | |----+----+----+----+----+----+----+----| 15m 00s | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | |----+----+----+----+----+----+----+----| 07m 30s | 57 | 58 | 59 | 60 | 61 | 62 | 63 | 64 | ----------------------------------------- 43d 00m 00s 92d 91d 00m 52m 45m 37m 30m 22m 15m 07m 00m 00s 30s 00s 30s 00s 30s 00s 30s 00s Figure 2: 3.75-minute quarters ----------------- | | | | 2 | 1 | | | | |-------|-------| | | | | 3 | 4 | | | | ----------------- Attribute Data The source of the attribute data is the Natural Resources Conservation Service Map Unit Interpretations Record data base. The attribute data give the proportionate extent of the component soils and their properties. The data contain both estimated and measured physical and chemical soil properties and soil interpretations for engineering, water management, recreation, agronomic, woodland, range, and wildlife uses of the soil. The attribute data are distributed in the following tables: CODES (data base codes) - stores information on all codes used in the data base COMP (map unit component) - stores information which will apply to a specific component of a soil map unit COMPYLD (component crop yield) - stores crop yield information for soil map unit components FEATURE (special soil features definition) - stores definitions for special soil point and line features FOREST (forest understory) - stores information for plant cover as forest understory for soil map unit components HELCLASS (highly erodible lands class) - stores the highly erodible land classification for wind and water assigned to the soil map units HYDCOMP (hydric component information) - stores data related to the hydric classification, criteria, and landform INCLUSN (map unit inclusion) - stores the name of soils included in the soil map units INTERP (interpretation) - stores soil interpretation ratings (both limitation ratings and suitability ratings) to soil map unit components LAYER (soil layer) - stores characteristics which apply to soil layers for soil map unit components MAPUNIT (map unit) - stores information which applies to all components of a soil map unit MUCOACRE (map unit county acres) - stores the number of acres for the map unit within a county MUYLD (map unit yield) - stores crop yield information for the soil map unit PLANTCOM (plant composition) - stores plant symbols and percent of plant composition associated with components of soil map units PLANTNM (plant name) - stores the common and scientific names for plants used in the data base RANGENM (range name) - stores the range site names RSPROD (range site production) - stores range site production information for soil map unit components SSACOAC (soil survey area county acreage) - stores the acreage for the county within the boundary of the soil survey area SSAREA (soil survey area) - stores information that will apply to an entire soil survey area TAXCLASS (taxonomic classification) - stores the taxonomic classification for soils in the data base WINDBRK (windbreak) - stores information on recommended windbreak plants for soil map unit components WLHABIT (wildlife habitat) - stores wildlife habitat information for soil map unit components WOODLAND (woodland) - stores information on common indicator trees for soil map unit components WOODMGT (woodland management) - stores woodland management information for soil map unit components YLDUNITS (yield units) - stores crop names and the units used to measure yield The attribute tables are simple variable record length ASCII text files. The first two lines of a table are called the header files. The first line contains the names of each column, and the second line contains at least one dash underneath each column name. Tabs separate the column names and the dashes. A return character is at the end of each of these lines. Each subsequent line (row) is also delimited by a return character and forms a record in the table. A row consists of tab-delimited fields (columns). Each row has the same number of columns as the table header. If a column is empty, two consecutive tabs indicate that the column is present. Arc Interchange --------------- The data are distributed by quadrangle and survey area wide extents in noncompressed Arc interchange format. Coordinate Reference Data coordinates for Arc interchange files vary with the geographic extent. Coordinates for quadrangle coverages are in UTM meters. Coordinates for survey area wide coverages are in Geographic decimal degrees. Both are referenced to the North American Datum of 1983. File Naming Convention Survey area wide coverages - The root file name is seven characters in length and consists of a two alpha character state abbreviation, a three integer survey code, an underscore character, and a one character id for the data type. (example ME031_a). The data type codes are as follows: a - soil polygons p - special soil point features l - special soil line features b - survey boundary polygons q - quadrangle grid polygons Quadrangle coverages - The file naming convention for SSURGO Arc interchange files follow the data set naming convention used in the USGS National Digital Cartographic Data Base, but with some modifications. A brief description of the naming convention follows: Sample File Name: tyyxxxzz_qt t - indicates type of data (s = SSURGO) yy - indicates southeast latitude of the one-degree block in which the quadrangle resides xxx - indicates southeast longitude of the one-degree block in which the quadrangle resides zz - is the 7.5-minute section number of the one- degree block in which the quadrangle resides (reading left to right from northwest corner) _q - indicates the 3.75-minute quarter of the 7.5- minute quadrangle expressed as an integer (7.5-minute quadrangles are coded as "0") NE - 1 NW - 2 SW - 3 SE - 4 t - indicates data type a - soil polygons p - special soil point features l - special soil line features Example 1: Quarter Quadrangle s4309101_2a - a soil polygon Arc interchange file, for the northwest 3.75-minute quarter of the first 7.5-minute quadrangle of the one-degree block, whose southeast corner is 43-degrees north latitude and 91-degrees west longitude. Example 2: Full Quadrangle s4309125_0a - a soil polygon Arc interchange file, for the 7.5-minute quadrangle whose southeast corner is 30 minutes and 00 seconds north latitude and 52 minutes and 30 seconds west longitude of the one-degree block, whose southeast corner is 43-degrees north latitude and 91-degrees west longitude. Attribute Data For a description of the attribute data, see Attribute Data in the section describing DLG-3 data format above. Attribute data are distributed in noncompressed Arc interchange format. Metadata ======== A metadata textfile is distributed with each SSURGO data set. The metadata textfile provides information on the content, quality, condition, and other characteristics of the data. Metadata are compliant to the Federal Geographic Data Committee, 1994, Content Standards for Digital Geospatial Metadata. ##########################################################################