Alexander C. Seymour Kara S. Doran Margaret L. Palmsten 20260310 1.0 vector digital data Alexander C. Seymour Kara S. Doran Margaret L. Palmsten 20260310 U.S. Geological Survey data release doi:10.5066/P9GL68X8 St. Petersburg, FL U.S. Geological Survey - St. Petersburg Coastal and Marine Science Center 2026a https://doi.org/10.5066/P9GL68X8 The U.S. Geological Survey (USGS) supports multiple efforts to understand and predict storm impacts to our nation's coastlines. The first infrastructure line is defined as the seaward boundary of the first row of structures or roads in a coastal area and can be used to assess coastal vulnerability. The first infrastructure line as defined in this dataset represents a cross shore boundary where the most intense hold-the-line management actions are likely to be taken to prevent further landward transgression of the foredune. Certain built features, which often extend far seaward from primary residences and commercial buildings, including boardwalks, swimming pools, gazebos, and sheds, are not included in this first infrastructure line. This dataset is optimized for use in measuring the distance between the first infrastructure line and seaward protective features, particularly coastal dunes. The first infrastructure line in North Carolina (NC) was digitized along the developed ocean-fronting portion of the coastline using imagery/orthomosaics collected by the National Agriculture Imagery Program (NAIP), National Geodetic Survey (NGS), and the Environmental Systems Research Institute (Esri)between 8/26/2018 and 7/16/2021. To provide the seaward boundary of the first infrastructure line as a vector shapefile (.shp). The methods used to digitize these data are described in "Decadal-scale characteristics of natural and anthropogenic dune morphology along North Carolina barrier islands (SE Atlantic coast)" by Seymour and others (2026b) and are also described in the process steps of this metadata record. 20180826 20210913 ground condition Complete None planned -78.516845 -75.461508 36.5496588 33.843362 USGS Metadata Identifier USGS:daf5f6fc-198c-4bab-b400-3d868789b833 ISO 19115 Topic Category geoscientificInformation oceans environment structure USGS Thesaurus hazards marine geology ocean sciences coastal processes erosion floods geospatial datasets None U.S. Geological Survey USGS St. Petersburg Coastal and Marine Science Center SPCMSC Coastal and Marine Hazards and Resources Program CMHRP Coastal Change Hazards CCH Geographic Names Information System (GNIS) North Carolina Atlantic Ocean None Public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. The U.S. Geological Survey requests to be acknowledged as originators of the data in future products or derivative research. U.S. Geological Survey - St. Petersburg Coastal and Marine Science Center Kara S. Doran mailing and physical

600 4th Street South

Saint Petersburg FL 33701 United States 727-502-8117 727-502-8001 kdoran@usgs.gov Windows 10 Enterprise 21H2 (Build 19044.1826); Esri ArcGIS Pro 2.7.1 Alexander C. Seymour Daniel J. Ciarletta Kara S. Doran Margaret L. Palmsten 20260305 Journal of Coastal Research Unknown 2026b https://doi.org/10.2112/JCOASTRES-D-25-00053.1 Chelsea A. Stalk Karen L.M. Morgan Jenna A. Brown Christopher R. Sherwood 20200408 U.S. Geological Survey data release doi:10.5066/P9R9DPFS St. Petersburg, Florida U.S. Geological Survey - St. Petersburg Coastal and Marine Science Center https://doi.org/10.5066/P9R9DPFS Jenna A. Brown Christopher R. Sherwood Marinna Martini Christine J. Kranenburg Jin-Si R. Over 20210408 U.S. Geological Survey data release doi:10.5066/P9DVZC23 St. Petersburg, Florida U.S. Geological Survey - St. Petersburg Coastal and Marine Science Center https://doi.org/10.5066/P9DVZC23 North Carolina Department of Environmental Quality 1974 Raleigh, NC North Carolina Department of Environmental Quality https://deq.nc.gov/about/divisions/coastal-management/coastal-management-rules-regulations/coastal-area-management-act No formal logical accuracy tests were conducted. This dataset is considered complete for the information presented, as described in the abstract section. Alongshore gaps are present in the first infrastructure line vector where no infrastructure exits within 500 m of the shoreline. Users are advised to read the rest of the metadata record carefully for additional details. Cumulative cross shore positional uncertainties of the first infrastructure line are provided for each segment. In this study, cumulative uncertainty is the summation of the georeferencing error of the utilized source imagery, one half of the pixel resolution of the source imagery, and the digitizing error. The National Oceanic Atmospheric Administration (NOAA) NGS imagery georeferencing error is represented by the horizontal error published with the source imagery. The Esri basemap imagery (collected by the North Carolina CGIA) georeferencing error was derived from 11 checkpoints in Onslow Bay, NC and 16 checkpoints in the Northern Outer Banks, NC that were recorded in 2019 and published in two different surveys: Stalk and others (2020); Brown and others (2021). The United States Department of Agriculture (USDA) NAIP imagery georeferencing errors were derived by comparing the positional offset of recognizable and discrete marks (such as tennis court, parking space, and crosswalks) on the ground between the Esri basemap (treated as a control) and NAIP imagery. Twenty-seven marks in Onslow Bay and 15 in the Northern Outer Banks were used for this purpose. NAIP imagery georeferencing errors are the positional offsets from the marks on the control, plus the georeferencing error of the Esri basemap imagery from the respective Onslow Bay or Northern Outer Banks region. The control points recorded in 2019 could not be used to measure the error of the NAIP imagery because not enough control points from the survey were visible in the NAIP imagery. Digitizing errors were derived by re-digitizing an additional first infrastructure line across 20.4 kilometers (km) on Oak Island, NC. The cross-shore distance between the original infrastructure line and the second infrastructure line was recorded at 10 meters (m) alongshore intervals. The digitizing error is the mean of the cross-shore distances recorded on these transects (0.99 m). All editing and calculations were conducted in ArcGIS Pro version 2.7. The final dataset is projected to the North American Datum of 1983 (NAD 1983) National Spatial Reference System (NSRS2007) Universal Transverse Mercator Zone 18 North (UTM 18N) coordinate system. North Carolina Center for Geographic Information and Analysis 20151113 ArcGIS Online Esri https://www.arcgis.com/home/item.html?id=28f49811a6974659988fd279de5ce39f raster digital data 20200115 20210913 ground condition Esri basemap Orthomosaics were used to reference the seaward boundary of the first infrastructure line during manual digitization, and to identify qualifying and non-qualifying structures. United States Department of Agriculture National Agriculture Imagery Program 20191226 Charleston, SC NOAA https://www.fisheries.noaa.gov/inport/item/58387 raster digital data 20180826 20181222 ground condition USDA NAIP imagery Orthomosaics were used to reference the seaward boundary of the first infrastructure line during manual digitization, and to identify qualifying and non-qualifying structures. National Oceanic and Atmospheric Administration National Geodetic Survey 202203 Charleston, SC NOAA Office for Coastal Management, National Geodetic Survey https://www.fisheries.noaa.gov/inport/item/66699 raster digital data 20200105 20200417 ground condition NOAA NGS imagery Orthomosaics were used to reference the seaward boundary of the first infrastructure line during manual digitization, and to identify qualifying and non-qualifying structures. Several sets of aerial and satellite imagery were used as a reference for this digitizing project, including imagery/orthomosaics from Esri, USDA NAIP, and NOAA NGS. Survey dates for the reference imagery range from 8/26/2018 to 9/13/2021. The imagery set used for a given reach of coast was determined by the available imageries’ perspective, published error, and pixel resolution. A purely nadir perspective (viewing angle directly perpendicular to the earth’s surface) of buildings, or an off-nadir viewing angle that allowed for the seaward facing side of a structure to be visible was required for an image to be used for digitization. Among images that satisfied this perspective requirement, imagery with more constrained horizontal errors and finer pixel resolutions were preferred. Esri basemap USDA NAIP imagery NOAA NGS imagery 20211101 Alexander C. Seymour U.S. Geological Survey - St. Petersburg Coastal and Marine Science Center Physical Scientist mailing and physical

600 4th Street South

Saint Petersburg FL 33701 United States 727-502-8122 727-502-8001 aseymour@usgs.gov Digitization was conducted by a single researcher at 1:1,300 – 1:550 mapping scales in ArcGIS Pro version 2.7. The ArcGIS Pro editor toolbar was used to draw polylines alongshore. The first infrastructure line as defined in this dataset represents a cross-shore boundary where the most intense hold-the-line management actions are likely to be taken to prevent further landward transgression of the foredune. As such, digitization of this line required basic review of state statutes; in this case, the North Carolina Coastal Area Management Act of 1974 (North Carolina Department of Environmental Quality, 1974). According to North Carolina state statute, certain built structures can be classified as “threatened structures”, which can qualify them for elevated levels of protection including geotextile sandbag armoring. However, certain built features which often extend far seaward from primary residences and commercial buildings cannot be designated as “threatened structures”, including boardwalks, swimming pools, gazebos, and sheds. Thus, the aforementioned built features were ignored during digitization. This product was generated to facilitate calculation of coastal resilience metrics, specifically the distance between the dune crest and first infrastructure line. In some circumstances, limited, intermittent coastal retreat can occur among the line of first infrastructure, resulting in isolated clusters of buildings with more seaward positions than immediately adjacent dune crests. To ensure that dune crest/infrastructure distances derived from this data can be sensitive to this condition, we connected alongshore gaps in the first infrastructure line less than 200 m long. This produced negative infrastructure/dune crest distances, which may indicate areas where the primary foredune is infiltrating the first infrastructure line. For more information, please refer to Seymour and others (2026b). 20211101 Alexander C. Seymour U.S. Geological Survey - St. Petersburg Coastal and Marine Science Center Physical Scientist mailing and physical

600 4th Street South

Saint Petersburg FL 33701 United States 727-502-8122 727-502-8001 aseymour@usgs.gov Uncertainty, source imagery, and state attributes were added to the attribute table of the digitized first infrastructure line segments using ArcGIS Pro's "Add Field" function and manual entry of values. ArcGIS Pro version 2.7 was used for these processes. 20221219 NC_First_Infrastructure_Line.shp Alexander C. Seymour U.S. Geological Survey - St. Petersburg Coastal and Marine Science Center Physical Scientist mailing and physical

600 4th Street South

Saint Petersburg FL 33701 United States 727-502-8122 727-502-8001 aseymour@usgs.gov Vector String 44 Universal Transverse Mercator 18N 0.9996 -75.0 0.0 500000.0 0.0 coordinate pair 0.001 0.001 meters NAD 1983 (NSRS2007) GRS 1980 6378137.0 298.257222101 NC_First_Infrastructure_Line.shp Polyline shapefile of the first infrastructure line for North Carolina. USGS FID Internal feature number. Esri Sequential unique whole numbers that are automatically generated. Shape Feature geometry. Esri Coordinates defining the features. Shape_Leng Length of line segment, in meters. Esri 155.610335 45904.093541 Segment First infrastructure line segment identification number, ordered from north to south. USGS 1 44 Source_Img Character string representing the publisher of the imagery sources used to digitize the first infrastructure line on a given segment. If multiple sources were used, each were separated by a comma. USGS ESRI Esri basemap imagery was used to digitize the first infrastructure line segment. USGS USDA USDA NAIP imagery was used to digitize the first infrastructure line segment. USGS NGS NOAA NGS imagery used to digitize the first infrastructure line segment. USGS State Character string representing the state where the segment is found. USGS North Carolina The state where the segment is located. USGS Uncy A string representing the cross-shore positional uncertainty of the first infrastructure line, in meters. An uncertainty is provided for each imagery source used on a given segment. USGS The uncertainty for each source image used separated by a comma. The order of the provided uncertainties follows the order of the source images listed in the Source_Img attribute. U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center USGS SPCMSC Data Management mailing and physical

600 4th Street South

Saint Petersburg FL 33701 United States 727-502-8000 gs-g-spcmsc_data_inquiries@usgs.gov NC_First_Infrastructure_Line.shp Neither the U.S. Government, the Department of the Interior, nor the USGS, nor any of their employees, contractors, or subcontractors, make any warranty, express or implied, nor assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, nor represent that its use would not infringe on privately owned rights. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data or related materials. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), and have been processed successfully on a computer system at the USGS, no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty. The USGS or the U.S. Government shall not be held liable for improper or incorrect use of the data described and/or contained herein. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. shapefile The data download file is compressed and must be unzipped using software such as WinZip, 7Zip, etc. before use. https://coastal.er.usgs.gov/data-release/doi-P9GL68X8/data/NC_First_Infrastructure_Line.zip None None 20260310 U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center USGS SPCMSC Data Management mailing and physical

600 4th Street South

Saint Petersburg FL 33701 United States 727-502-8000 gs-g-spcmsc_data_inquiries@usgs.gov Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998 local time