What Is a Soil Survey?

Every soil result on this site comes from USDA’s soil survey: more than a century of fieldwork turned into maps of about 2.3 billion acres. Below: how a survey is made, the five kinds the Soil Survey Manual describes, how to read one and use Web Soil Survey, and where its limits are.^[1][2]

See the survey record for a spot

Enter a US address, city or ZIP, or tap the map, to read USDA’s survey record for that exact point: the survey area, the map unit, its soils and their shares.

US addresses only: street address, city and state, or ZIP.

A soil survey is an inventory of the soils in an area: soil scientists walk the land, describe and sample the soil, test samples in a laboratory, and draw maps of soil areas called map units. USDA’s soil survey began in 1899, and its detailed digital form, SSURGO, now covers about 2.3 billion acres in 3,386 survey areas.

How a soil survey is made

The information was gathered by walking over the land and observing the soil, and many samples were analyzed in laboratories. The maps outline map units, drawn at scales from 1:12,000 to 1:63,360, with more detail at 1:12,000. A survey area is a single county, several counties, or parts of counties, and the data is bundled by survey area.^[2][3]

A survey is made by walking the land and observing the soil, with samples analyzed in laboratories, and its maps outline the soil areas called map units.^[3]

A short history

On May 3, 1899, Congress funded USDA to investigate the nation’s soils in the field and the laboratory. By the end of that year USDA had mapped 720,000 acres and published four surveys: Cecil County, Maryland; the Connecticut Valley in Connecticut and Massachusetts; the Salt Lake Valley of Utah; and the Pecos Valley of New Mexico. Today NRCS leads the work through the National Cooperative Soil Survey.^[4][1] 3,386 survey areas now hold digital SSURGO data.^[2]

Types of soil survey: orders 1 to 5

Not every survey is mapped in the same detail. USDA’s Soil Survey Manual describes five orders of soil survey, from order 1, very detailed information for small areas, to order 5, soil information for very large areas. Each order fits a different use, base map scale and kind of map unit; the manual calls the scales general ranges.^[5]

Order	Used for	Typical base map scale	Map units
1	Very detailed soil information, generally for small areas; the land uses commonly need reviews and permits from regulatory agencies, engineers and other professionals	1:15,840 or larger, up to 1 inch = 20 feet (1 cm = 15 m)	Typically consociations, with no more than 15% dissimilar minor components
2	Planning for general agriculture, construction, urban development and similar uses	1:12,000 to 1:31,680, depending on how complex the soil pattern is	Mostly consociations and complexes; may include undifferentiated groups or associations
3	Land uses that don't need precise knowledge of small areas: planning for range, forest and recreation areas, and community planning	1:20,000 to 1:63,360	Associations, complexes, consociations and undifferentiated groups
4	Locating, comparing and selecting suitable areas for major kinds of land use	1:63,360 to 1:250,000	Mostly associations; some consociations and undifferentiated groups
5	Soil information for very large areas, used mainly to select areas for more intensive study	About 1:250,000 to 1:1,000,000 or smaller	Typically associations; may include some consociations and undifferentiated groups

To read a scale, the bigger the second number, the less detail: 1:63,360 is 1 inch to 1 mile (1 cm to 634 m), while 1:250,000 is 1 inch to 3.9 miles (1 cm to 2.5 km).^[5]

SSURGO and STATSGO2

USDA publishes two digital soil maps of the country at very different scales. SSURGO is drawn at 1:12,000 to 1:63,360.^[2]

STATSGO2, the Digital General Soil Map of the United States, is a broad-based inventory of soils and non-soil areas, made by generalizing more detailed soil survey maps. Its scale is 1:250,000 in the continental US, Hawaii, Puerto Rico and the Virgin Islands, and 1:1,000,000 in Alaska, and it’s designed for broad planning and management across state, regional and multi-state areas. It supersedes the older STATSGO dataset.^[6]

Every soil figure on this site comes from the detailed SSURGO surveys; STATSGO is left out.^[2] For a property, the detailed map is the one to read, and even it describes areas rather than single spots; see what a soil survey can’t tell you.

What’s in the survey

The survey in numbers, from our aggregation of USDA’s data:^[2]

Survey areas	3,386
Map units	331,762
Components	1,204,944
Distinct series names in the data	27,654
Total acres	2.3 billion acres

Acres by kind of component

Kind	Acres	Share
Classified soils	1.9 billion	83.5%
Miscellaneous areas	215 million	9.4%
No mineral layer data	91 million	4.0%
Organic soils (Histosols)	49 million	2.1%
No Digital Data Available	23 million	1.0%

Shares of total surveyed acres.

The 10 most widespread soil series

Series	Acres	Most acres in
Valentine	10.8 million	Nebraska
Gilpin	5.8 million	West Virginia
Smithdale	5.7 million	Mississippi
Cecil	5.5 million	Georgia
Williams	4.2 million	North Dakota
Ector	4.0 million	Texas
Harney	3.9 million	Kansas
Sharkey	3.7 million	Louisiana
Valent	3.5 million	Colorado
Berks	3.2 million	West Virginia

A series is the lowest level of USDA’s soil classification, and NRCS’s national collection holds more than 20,000 official series descriptions, a different count from the 27,654 distinct series names in the survey data above.^[7] The soil orders page explains the levels above the series.

Download the data: acres by kind (CSV).

What a record holds

Each record holds available water capacity, soil reaction (pH), electrical conductivity, flooding frequency, yields for cropland, woodland, rangeland and pasture, and limitations for building and other engineering uses.^[3] We turn these into plain-language checks: the water table, septic and building checkers, and the soil’s pH in each address result. Its cropland ratings drive the soil quality map and prime farmland map. Each soil’s horizons, its texture of sand, silt and clay, and the material it formed in, such as alluvium, come from the same records.

How to read a map unit

The name gives the main soil (Clarion), its surface texture (loam) and its slope range. The percentages are each soil’s share of the map unit. A map unit holds one to three major soils plus some minor ones.^[3] Names that join soils with a hyphen, such as Urban land-Flatbush complex, describe areas where those soils occur together.

Example map unit

Clarion loam, Bemis moraine, 2 to 6 percent slopes

Clarion85%
Storden10%
Nicollet5%

Source: USDA NRCS soil survey (SSURGO), via Soil Data Access.

A map unit is named for its main soil but holds other soils too, so one spot can differ from the name on the map.^[3][2]

What a soil survey can’t tell you

USDA intends the maps for natural resource planning by landowners, townships and counties, and notes that some knowledge of soils data and map scale is needed to avoid misunderstandings.^[3] A map unit describes an area, not a single spot: your yard may sit on one of the minor soils, or on ground that was graded or filled. We treat the survey as a first check, not a site investigation. For a septic system, a foundation or a land purchase, have the site evaluated in person.

Web Soil Survey, Soil Data Access and this site

USDA publishes SSURGO through Web Soil Survey, its official app, and through Soil Data Access, a set of web services.^[2][8] This site reads SSURGO live from Soil Data Access and turns it into plain-language answers; the methodology page explains each step.

Using Web Soil Survey in four steps

NRCS’s how-to guide breaks it into four steps:

Define an area of interest (AOI).
View the soil map.
Explore the data.
Check out: build a custom report for the area. It’s free, and you can view or print it as a PDF.^[9]

For a single point, the lookup at the top of this page reads the same record without drawing an area first.

Frequently asked questions

What is a soil survey?: A soil survey is an inventory of the soils in an area: soil scientists walk the land, describe and sample the soil, test samples in a laboratory, and draw maps of soil areas called map units.^[3]
Who makes soil surveys in the US?: USDA's Natural Resources Conservation Service leads them through the National Cooperative Soil Survey, with other federal agencies, state and local governments and other cooperators.^[10]
How do I use Web Soil Survey?: NRCS's guide gives four steps: define an area of interest, view the soil map, explore the data, then check out a custom report. The report is free, and you can view or print it as a PDF.^[9]
What is SSURGO?: The Soil Survey Geographic Database: USDA's detailed digital soil survey data, mapped at scales from 1:12,000 to 1:63,360 and bundled by survey area.^[2]
What are the types of soil survey?: The Soil Survey Manual describes five orders. Order 1 gives very detailed information, generally for small areas, at 1:15,840 or larger; order 5 covers very large areas at about 1:250,000 to 1:1,000,000 or smaller, mainly to pick areas for more intensive study.^[5]
What is the difference between SSURGO and STATSGO2?: Scale and purpose. SSURGO is mapped at 1:12,000 to 1:63,360. STATSGO2, the Digital General Soil Map of the United States, was made by generalizing more detailed soil survey maps; it's mapped at 1:250,000 (1:1,000,000 in Alaska) for broad planning across state, regional and multi-state areas.^[2][6]
When did the US soil survey start?: On May 3, 1899, Congress funded USDA to investigate the nation's soils in the field and the laboratory. By the end of that year USDA had mapped 720,000 acres and published four surveys.^[4][1]
How old is the soil survey for my area?: Enter your address in the lookup at the top of this page: the record shows your survey area and the date of USDA's current data for it.
Is a soil survey the same as a soil test?: No. A soil survey maps and describes the soils of a whole area; a soil test analyzes a sample you take from your own ground.

How we calculate this

Every count comes from the SSURGO component rows we read from USDA Soil Data Access across 3,386 detailed survey areas; STATSGO is excluded. Component acres are map-unit acres times the component’s representative percent. Map-unit purity is the acre-weighted spread of the largest component’s percent within each map unit. Data generated 2026-10-07.^[2]

Sources

Marko Visic · MPharm, BSc Physics · Last reviewed November 13, 2026