GLOSSARY
The words behind the numbers.
A quick reference for reading your report without confusing a soil property with a building diagnosis.
- Linear extensibility (LE)
A reported percentage expression of soil length change between defined moist and dry conditions. It describes a soil property, not the probability of building damage.
USDA NRCS linear-extensibility definitions- Map unit
A mapped area described by a mixture of soil and other components. It is not a survey of the exact soils beneath one building.
USDA SSURGO- Dominant component
Our highlighted, uniquely largest reported component in a single returned map unit. If shares tie or map units overlap, we do not select a unique dominant component.
USDA Soil Data Access- Soil horizon
A soil layer with reported upper and lower depth boundaries and, where available, property values. Our screening window is 0–100 cm.
USDA Soil Data Access- Rated depth
The total non-overlapping portion of the upper 100 cm that has a reported linear-extensibility value. Unrated depth remains unknown.
USDA Soil Data Access- Clay percentage
The reported clay-sized fraction in a soil layer. Clay percentage and linear extensibility are not interchangeable.
USDA Soil Data Access- Plasticity index
The difference between liquid and plastic limits. It is a separate soil characteristic, not a percentage chance of damage.
USDA Soil Data Access- Drainage class
A reported soil-survey drainage characteristic. It is not a test of the gutters, pipes or drains at a particular property.
USDA SSURGO- D1 or worse
County area in moderate drought or a more intense category. It does not measure the fraction of your property affected.
Drought category definitions- Cumulative drought coverage
Higher-intensity categories are included within the less intense categories. D0 through D4 percentages overlap and must not be added.
U.S. Drought Monitor data- Percentage points
An absolute difference between percentages. A change from 20% to 50% is +30 percentage points. It is not a 30% increase in property risk.
U.S. Drought Monitor data- Source date vs. retrieval date
The source date describes the dataset or map vintage. Retrieval time describes when we fetched it. Fetching an old source today does not make it current.
USDA Soil Data Access- No data
A limitation in the evidence, not a low rating or an assurance of safety. An outage, missing coverage and an unrated property are different states.
USDA SSURGO
FROM A QUESTION TO A CLEARER PICTURE
Know the evidence. Know your next step.
Start with the ground, add your observations and keep the two separate.