Shorelines used to calculate shoreline change statistics from the North Shore B coastal region from the Annisquam River in Gloucester to the west side of Deer Island in Boston Harbor (NorthShoreB_shorelines.shp)

Route identification value assigned to individual lidar shoreline line segments. A unique cross-shore profile identification value is stored at each vertex of the lidar route and serves as a common attribute to the shoreline uncertainty table.

Agency that provided shoreline feature or the data source used (e.g. T-sheet) to digitize shoreline feature.

Date of shoreline position; date of survey as indicated on source material. A default date of 07/01 was assigned to shorelines where only the year was known (month and day unknown). Using July, the mid-point month of the calendar year, minimizes the potential offset to the actual shoreline date by a maximum of six months.

Estimate of shoreline position uncertainty. Actual shoreline position is within the range of this value (plus or minus, meters). Actual shoreline position is within the range of this value (plus or minus, meters). The method used to determine this uncertainty is described in the accompanying written report (Open-File Report 2012-1189) under the section titled "Estimation of Shoreline Position Uncertainty" (https://pubs.usgs.gov/of/2012/1189). The historic shoreline uncertainty values contain all of the measurement errors listed in Table 2 of OFR 2012-1189, except for the uncertainty of the High Water Line (HWL). The HWL uncertainty listed in Table 2 was averaged for the entire state (4.3). However, the uncertainty of the HWL at an individual transect can be determined with more precision along the shoreline route. The HWL uncertainty was added to the historic shoreline uncertainty stored in the shoreline attribute table during the DSAS rate calculation process to better account for uncertainty at individual transects alongshore as opposed to using a regionally averaged value. This was done using linear referencing that interpolates a value based on data stored in the shoreline_uncertainty dBase file (.dbf) at a specific transect/shoreline intersect alongshore. The lidar shoreline position uncertainty is also stored in the associated shoreline_uncertainty.dbf file and values are interpolated at specific transect/shoreline intersections using the same linear referencing method. The lidar uncertainty attribute field was filled with null values while residing in the geodatabase. Upon exporting the shoreline feature class to a shapefile for publication, the null values in the lidar uncertainty field were automatically converted to zero values.

Differentiates between shorelines that have known month and day attributes and those that use the default value of 07/01 when only the year is known.

Length of feature/transect in meter units (State Plane Massachusetts Mainland FIPS 2001, NAD83)