North Carolina Dune Condition Codes

Methods for deriving spatial and time series data and attributes in this data release can be found in Seymour and others (2026). For final predicted dune crest elevations, if the dune crest was classified as increasing or decreasing in elevation across the time series, this value is the final dune crest elevation predicted by the regression at the end of the time series and the uncertainty is represented by the 95% prediction interval. If the dune crest was classified as no net change in elevation across the time series, this value is the mean dune crest elevation across the time series, and the uncertainty is represented by the 95% confidence interval for the time series mean. Final predicted dune crest cross-shore positions are not an independent attribute but were used during the calculation of the dune crest to infrastructure distance. For final predicted dune crest cross-shore positions, if the dune crest was classified as migrating seaward or landward across the time series, this value is the final dune crest position predicted by the regression at the end of the time series. If the dune crest was classified as no net change in position across the time series, this value is the mean dune crest position across the time series. For the final predicted 98% quantile total water level elevation, if 98% quantile total water level elevation was classified as increasing or decreasing across the time series, this value is the final elevation predicted by the time series regression, and the uncertainty is represented by the 95% prediction interval. If the 98% quantile total water level elevation was classified as no net change across the time series, this value is the mean 98% quantile total water level elevation across the time series, and the uncertainty is represented by the 95% confidence interval for the time series mean. In the above attributes, final predicted values and time series means were used because they correct for interannual dune elevation, position, and Q98 TWL variance better than the observed dune elevations from the latest survey year. See Seymour and others (2026) for more information. Additionally, after the dune condition code features were generated, an analyst manually removed select positions that occurred in inlets where the elevation of shoals was contributing datapoints to the time series. This sometimes occurs after the erosive loss of the subaerial beach and results in inaccurate dune elevation and migration change trends. Additional points were removed that were calculated from transects that diverged from shore-normal orientations. Specifically, this could occur most often directly on cape headlands, or on spits adjoined to cape headlands.

The data included in this release is a point feature class of the dune condition codes stored in a file geodatabase (.gdb), along with a comma-delimited ASCII table (.csv) for users that do not have the ability to open and view Geographic Information Systems (GIS) file formats. The dune condition code ASCII table was generated by inputting the geodatabase feature class into the ‘Feature Class to ASCII’ ArcGIS Pro geoprocessing tool.

To include additional visualizations of the feature class data, an ArcGIS Pro Map Package (.mpkx) was generated, which contains specific symbolization of the feature classes and charts that aid the user in interpreting and visualizing some of the most important attributes in the data. The geodatabase feature classes, both the dune condition code described in this metadata record (NC_Dune_Condition_Codes_GDB), and time series features (NC_Time_Series_Features_GDB, described in NC_Time_Series_Features_Metadata) were added to a new ArcGIS Pro map. Map symbology was established by setting the symbology type to Unique Values and selecting the ‘Elevation Condition’, ‘Elevation Trend’, and ‘Migration Trend’ fields, and classifying/coloring those symbol classes. The rational for the symbol types and colors are described in Seymour and Others (2024). Scatterplots displaying interannual dune elevation and cross shore position change were created by selecting the time series features and clicking on the scatter plot option under the Create Charts button within the Data toolbar tab. The ‘Survey Year’ field was chosen as the x-axis and the ‘Mean Dune Elevation’ or ‘Mean Dune Position’ was chosen as the y-axis. Bar charts displaying the frequency of dune condition codes were created by selecting the dune condition code features and clicking on the Bar Chart option under the Create Charts button within the Data toolbar tab. The ‘Condition Code’ field was chosen as the category variable and the Count option was chosen for aggregation. The Hybrid Reference Layer and World Imagery basemaps were also added to the map layout. For more information about these basemaps, refer to: Hybrid Reference Layer (https://www.arcgis.com/home/item.html?id=30d6b8271e1849cd9c3042060001f425) and World Imagery (https://services.arcgisonline.com/ArcGIS/rest/services/World_Imagery/MapServer). The map and its associated schema were then exported to a Map Package by clicking the ‘New Map Package’ command in the ‘Share’ tab in ArcGIS Pro.