Glossary

 

Agricultural Data: Data representing agricultural management practices including nitrogen fertilizer application, crop and livestock statistics, and agricultural land use. Represented as gridded data products or as county-level data. [top of page]

 

Atmospheric Deposition & Air Quality Data: Data for element deposition from the atmosphere, such as nitrogen and sulphur, and data regarding air quality parameters such astropospheric ozone, SOx, NOx, etc. Represented as gridded data products or as county-level data. [top of page]

 

Bounding rectangle of a polygon: The corners of a box in geographic coordinates that contains the entire polygon. These boundaries make up the outer North, South, East and West boundaries of the rectangle. [top of page]

 

Climate & Climatological Data: Data pertaining to modeled or measured physical climate variables and long-term climatological trends (precipitation, temperature, solar radiation, wind speed, vapor pressure, relative humidity, etc.), represented as either station-level data or gridded data products. [top of page]

 

Climatology (date class): Our climatology holdings contain data that represent averages over several years. For example, a climatology derived from monthly rainfall data for the period 1951 through 1980, might include 12 months of data, each the monthly average over that 30 year time period. Climatology data are often used to detect long-term trends or anomalies in climate conditions such as precipitation and temperature. EOS-WEBSTER classifies holdings according to temporal characteristics called "date class". Date classes are listed in our Data Guides. [top of page]

 

Collection: A grouping of data sets that all come from the same source, such as a modeling group, institution, or journal article. For example, all of the VEMAP2 data sets, produced by the National Center for Atmospheric Research (NCAR) have been grouped together into a single collection. A complete list of collections can be viewed on the Order Data page. [top of page]

 

Composite (date class): See Snapshot. [top of page]

 

Conterminous or Contiguous: Adjoining; refers to the 48 mainland United States of America (excludes Alaska and Hawaii). [top of page]

 

Data set: A subset of a collection that may be described as a single unit. Each data set may include one or more holdings. Data sets may contain a grouping of holdings that have been used together in a model to produce a set of model results. For example, the VEMAP2 collection includes the data sets TCLIMATE and TSCENARIO. Each of these data sets contain similar lists of holdings, such as fields for precipitation, temperature, and solar radiation. The range of years spanned and the origins of the data are different for each data set. Data sets for each collection can be viewed from the list of keywords on the collection Order Data page. [top of page]

 

Date class: A temporal characteristic for our data. Date classes include Climatology , Composite, Snapshot, and Time Series. Knowing the temporal characteristics of a collection will help you to make appropriate selections when ordering data from our system. Date classes are listed in our Data Guides. [top of page]

 

Demographic Data: Data representing modeled or measured socio-economic statistics, such as population. Represented as gridded data products or as county-level data. [top of page]

 

Domain: Describes political or geophysical boundaries. Domains include boundaries for continents, watersheds, counties, and any other spatial boundary. [top of page ]

 

Fill-value (or no-data value): A data value, usually a large negative number (such as -9999) that represents coordinates for which no data are available. For satellite imagery, fill values may also represent pixels that are not usable because of excess cloud cover or other problems. Data that are set to the fill-value should not be included in any statistics or other summary information about the data set. [top of page]

 

Forest Ecosystem & Carbon Dynamics Model Data: Data pertaining to modeled or measured forest ecosystem processes and physical variables, including carbon and carbon exchange such as net primary production, heterotrophic respiration, net ecosystem production, carbon storage in vegetation and in soils, net nitrogen mineralization, biomass, etc. Represented as gridded data products. [top of page]

 

Gazetteer: A place-name-index that links the name of an earth feature, such as a continent, watershed, county, or city, with its geographic location. The geographic location is represented by our system as a geographic coordinate or a polygon. Locations can be selected using the map interface on each collection's Order Data page to create spatial subsets of many of our data holdings. [top of page]

 

Grid-cell: A pixel representation of spatial data, where the entire area defined by the boundary of the grid-cell is represented by a single data value. For example, the VEMAP2 data are arranged by 0.5 x 0.5 degree latitude x longitude grid-cells, such that the USA is represented as 115 columns and 48 rows of data values. Grid-cells or pixels are the smallest spatial units of raster data sets. [top of page]

 

Holding: Consists of a single data file that can be ordered in its entirety or can be subsetted by time or spatial area. Examples of holdings are a single satellite image, or a hundred-year time series of monthly precipitation from a single source. [top of page]

 

Hydrologic Data & Water Demand: Data pertaining to the hydrologic cycle such as runoff, precipitation, soil moisture, evapotranspiration, etc., either modeled or measured, and water demand which is based on population statistics. Represented as gridded data products. [top of page]

 

Land Cover & Land Use Products: Modeled, measured, or satellite-derived estimates or classifications of land cover and land use, including vegetation cover and snow/ice cover. Represented as gridded data products or as raster imagery products. [top of page]

 

Raster data: A representation of a spatial data image as a two-dimensional array of numbers that represent pixels or grid-cells. The first row of pixels or grid-cells corresponds to the top row of the image, the second row of pixels to the second row of the image and so forth. [top of page]

 

Satellite Data Products: Satellite imagery, either radiances or reflectance data. Represented as raster imagery products. [top of page]

 

Satellite-derived Indices & Biophysical Parameters: Indices or biophysical parameters, either calculated or modeled from satellite imagery, such as Normalized Difference Vegetation Index (NDVI), Leaf Area Index (LAI), fraction of Photosynthetically Active Radiation (fPAR), etc. Represented as raster imagery products. [top of page]

 

Snapshot (date class): Data that represents a single period in time; such as an aerial photo, a satellite image, or an annual greenhouse gas inventory. A Composite is a particular type of snapshot that represents data aggregated over a time interval, such as eight days. Composites are commonly used for satellite imagery because it is unlikely that an entire region will be cloud-free on a single day. Date classes are listed in our Data Guides. [top of page]

 

Soils Data: Data pertaining to modeled or mapped soils properties, such as soil texture and soil properties, profiles and rooting depth, etc. Represented as gridded data, station data, or as county-level data. [top of page]

 

Spatial extent: The geographic domain of a data collection. For example, the spatial extent of the VEMAP2 collection is the United States. Knowing the spatial extent of a collection will help you to make appropriate spatial domain selections when searching for data in our system. [top of page]

 

Spatial resolution: Resolution is important in the ability to recognize and distinguish features. For raster data, the spatial resolution is the size of each grid-cell or pixel. For example, the VEMAP2 collection is made up of raster data for the USA at 0.5 degree latitude by longitude resolution. This means that the USA is divided into 0.5 degree grid-cells and each grid-cell is represented by a single data value. For vector data, the spatial resolution is the precision at which the location and shape of geographic features are stored. For example, a resolution of 1 meter means that the true ground position of a coordinate is within one meter of the stored coordinate values. [top of page]

 

Temporal characteristics: Data stored in our system may represent particular periods in time, or an average for a time-period, or may be a reference data layer. To distinguish these different temporal characteristics, data are classified by date class. Date classes include Climatology, Composite, Snapshot, and Time Series. Knowing the temporal characteristics of a collection will help you to make appropriate selections when ordering data from our system. Date classes are listed in our Data Guides. [top of page]

 

Temporal resolution: Resolution is important in the ability to recognize and distinguish features. Temporal resolution is a measure of time-step (time frequency) between data points. See Time-step for examples of temporal resolution. [top of page]

 

Time Series (date class): Holdings that represent multiple periods in time at a single time-step. Monthly precipitation data from 1960-2000 is an example of a time-series data. Time-steps of collections are listed in our Data Guides. [top of page]

 

Time-step: The time-step of Time Series data represents the temporal resolution of the data set. For example, the VEMAP2 collection contains data for the period 1895 - 2100 and has a monthly time-step. This means that data points represent an average value for the entire month. Examples of other common time-steps used in Earth System Science are daily, annual, and decadal. Time-steps for data that represent a single point in time are referred to as snapshots. Composites represent data collected at any time within a short time period, such as eight days. Time-step units are listed in our Data Guides. [top of page]

 

Trace Gas Emissions: Data representing the emission of gases, such as methane, from the land surface to the atmosphere, from either natural or anthropogenic sources. Represented as county-level data. [top of page]

 

Vector data: A coordinate-based spatial data structure, in which geographic boundaries are represented by a series of lines and vertices. A series of connected lines and vertices make up a polygon. [top of page]