The data variables within this data base have been placed into five data groups (i.e., three primary groups and two supplemental data groups). A quick reference listing of these data groups and variables is contained in Appendix A. The following terminology is used throughout this documentation.

**Data variable**--A single, discrete data item within a data group or data set (e.g., data set=elevation, data variable=mean elevation).**System variable**--A numeric variable that geographically identifies data variables within a data group.**Data set**--A collection of data variables that have been derived from a single data source, such as the mean and maximum elevation variables.**Data group**--A collection of data variables that have been placed into a single ARC/INFO export file and a comparable flat ASCII file.**Data base**--All data groups within this NDP.**Original data variables**--The 22 data variables from the seven data sets presented within this NDP [i.e., mean, maximum, and minimum elevation, and the number of 5´ National Geophysical Data Center (NGDC) grid cells used in deriving the data values; geology; geomorphology; relative sea-level trend, long-term geologic trend, corrected sea-level trend, local subsidence trend, and years of record of the gauge stations used in calculating these values; mean, maximum, and minimum shoreline displacement, and the number of 3´, 7.5´, or 15´ grid cells used in deriving the data values; mean and maximum tidal range, mean tide level, and the number of tide gauge stations used in calculating these variables; the 20-year mean wave height, maximum significant wave height and its standard deviation].**Relative risk variables**--The 7 classified risk variables derived from each of the following: mean coastal elevation, geology, geomorphology, local subsidence trend, mean shoreline displacement, mean tidal range, and maximum significant wave height.

Each of the five data groups within this NDP is stored as an exported ARC/INFO coverage and as a flat ASCII file.

The first two primary data groups are referenced to a 0.25° latitude by 0.25° longitude grid and stored as exported ARC/INFO polygon coverages and as flat ASCII files. The first group contains the original 22 data variables, while the second contains the 7 relative risk data variables. The grid system used covers the West Coast of the U.S. and is outlined by the following coordinates: 126°W, 32°N; 126°W, 49°N; 116°W, 49°N; and 116°W, 32°N. The grid origin (i.e., grid cell number 1) is at 126°W, 32°N, and cell identification numbers increase from left to right, bottom to top (Fig. 2a, 2b, and 2c).

The third data group offers the 29 data variables in their original line-based format. The data values in this data group may vary slightly from those in the gridded data groups since more than one line segment often fell within a single grid cell.

Nine of the 29 data variables within this data base were originally obtained as point data, and constitute the first supplemental data group. These data variables are stored in an exported ARC/INFO point coverage and as a flat ASCII file. Each data point is the physical location of the data measure (e.g., latitude-by-longitude location). Data variables within this group include: station name/number, latitude/longitude location, period of record, and the measurements used to derive the relative sea-level trend, long-term geologic trend, corrected sea-level trend, local subsidence trend, mean tidal range, maximum tidal range, and mean-tide-level variables.

The second supplemental data group contains a 1:2,000,000 digitized coastline of the U.S. West Coast. The coastlines were extracted from a map originally digitized by the USGS. This base map is intended to be used with the gridded data to provide locational information. These data are stored as an exported ARC/INFO line coverage and as a flat ASCII file. The line segments, and their identification numbers, are identical to those used in the first supplemental data group.