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Data Glossary

Agriculture Exposure Value

Agriculture exposure value refers to the estimated dollar value of crops and livestock determined to be exposed to a hazard according to a hazard-specific methodology.

Annualized Frequency

Annualized frequency is a natural hazard incidence factor for Expected Annual Loss, a risk component of the National Risk Index. It is the expected frequency or probability of a hazard occurrence per year.

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An Avalanche is a mass of snow in swift motion traveling down a mountainside.

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Building Exposure Value

Building exposure value refers to the dollar value of the buildings determined to be exposed to a hazard according to a hazard-specific methodology.

Census Blocks

Census blocks are statistical areas bounded by visible features—such as streets, roads, streams, and railroad tracks—and nonvisible boundaries—such as selected property lines and city, township, school district, and county boundaries. Census blocks are the smallest geographic area for which the U.S. Census Bureau collects and tabulates decennial Census data.

Census Tracts

Census tracts are small, relatively permanent statistical subdivisions of a county or equivalent entity that is updated by local participants prior to each decennial Census as part of the U.S. Census Bureau’s Participant Statistical Areas Program. The primary purpose of Census tracts is to provide a stable set of geographic units for the presentation of statistical data.

Coastal Flooding

Coastal Flooding is when water inundates or covers normally dry coastal land as a result of high or rising tides or storm surges.

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Cold Wave

A Cold Wave is a rapid fall in temperature within 24 hours and extreme low temperatures for an extended period.

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Community Resilience

Community Resilience is a consequence reduction risk component and community risk factor that represents the ability of a community to prepare for anticipated natural hazards, adapt to changing conditions, and withstand and recover rapidly from disruptions.

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Consequence Types

Consequences of natural hazard occurrences are categorized into three different types: buildings, population, and agriculture.


A Drought is a deficiency of precipitation over an extended period of time resulting in a water shortage.

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An Earthquake is a shaking of the earth's surface by energy waves emitted by slowly moving tectonic plates overcoming friction with one another underneath the earth's surface.

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Expected Annual Loss

Expected Annual Loss (EAL) is a natural hazards component of the National Risk Index that represents the average loss in dollars to buildings, population, and/or agriculture (consequence types) each year due to natural hazards.

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Exposure is a natural hazard consequence factor for Expected Annual Loss, a risk component of the National Risk Index. It is the representative value of buildings, population, or agriculture potentially exposed to a natural hazard occurrence.

Fishnet Grid

A fishnet grid is a geographic information system (GIS) feature containing a net of rectangular cells that can be used for sampling locations or as aggregation areas.

Geographic Information Systems (GIS)

A geographic information system (GIS) is a database system with software that can analyze and display data in a visual environment using digitized maps and tables. Maps and data may be layered, displayed, edited, and analyzed in a wide variety of ways.


Hail is a form of precipitation that occurs during thunderstorms when raindrops, in extremely cold areas of the atmosphere, freeze into balls of ice before falling towards the earth's surface.

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Related Terms

Hurricane, Natural Hazards

Heat Wave

A Heat Wave is a period of abnormally and uncomfortably hot and unusually humid weather typically lasting two or more days with temperatures outside the historical averages for a given area.

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Related Terms

Drought, Natural Hazards, Wildfire

Historic Loss Ratio

Historic loss ratio (HLR) is a natural hazard consequence factor of the Expected Annual Loss component of the National Risk Index. It is a hazard- and county-specific estimate of the percentage of the exposed consequence type (building value, population, or agriculture value) expected to be lost due to a hazard occurrence.


A Hurricane is a tropical cyclone or localized, low-pressure weather system that has organized thunderstorms but no front (a boundary separating two air masses of different densities) and maximum sustained winds of at least 74 miles per hour (mph).

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Ice Storm

An Ice Storm is a freezing rain situation (rain that freezes on surface contact) with significant ice accumulations of 0.25 inches or greater.

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A Landslide is the movement of a mass of rock, debris, or earth down a slope.

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Lightning is a visible electrical discharge or spark of electricity in the atmosphere between clouds, the air, and/or the ground often produced by a thunderstorm.

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Population Exposure

Population exposure refers to the estimated number of people determined to be exposed to a hazard according to a hazard-specific methodology.


A raster consists of a matrix of cells (or pixels) organized into rows and columns (or a grid) where each cell contains a value representing information. The cell values represent the phenomenon portrayed by the raster dataset, such as category or magnitude.

Riverine Flooding

Riverine Flooding is when streams and rivers exceed the capacity of their natural or constructed channels to accommodate water flow and water overflows the banks, spilling out into adjacent low-lying, dry land.

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Social Vulnerability

Social vulnerability is a consequence enhancing risk component and community risk factor that represents the susceptibility of social groups to the adverse impacts of natural hazards, including disproportionate death, injury, loss, or disruption of livelihood.

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Strong Wind

Strong Wind consists of damaging winds, often originating from thunderstorms, that are classified as exceeding 58 miles per hour (mph).

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A Tornado is a narrow, violently rotating column of air that extends from the base of a thunderstorm to the ground and is visible only if it forms a condensation funnel made up of water droplets, dust and debris.

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A Tsunami is a wave, or series of waves, generated by an Earthquake, Landslide, volcanic eruption, or even a large meteor hitting the ocean and causing a rise or mounding of water at the ocean surface. A Tsunami can travel across open ocean at about 500 miles per hour (mph), and slow down to about 30 mph as it approaches land, causing it to grow significantly in height.

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Value of Statistical Life (VSL)

Monetary value of preventing one statistical death. Within the National Risk Index, a VSL of $7.4M per fatality or 10 injuries is used to monetize population losses so that a total expected annual loss value can be computed that considers losses to buildings, population, and agriculture.

Volcanic Activity

Volcanic Activity occurs via vents that act as a conduit between the Earth’s surface and inner layers, and erupt gas, molten rock and volcanic ash when gas pressure and buoyancy drive molten rock upward and through zones of weakness in the Earth’s crust.

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A Wildfire is an unplanned fire burning in natural or wildland areas such as forests, shrub lands, grasslands, or prairies.

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Winter Weather

Winter Weather consists of winter storm events in which the main types of precipitation are snow, sleet or freezing rain.

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