1970s Shorelines for the Main Island of Puerto Rico

Shoreline Change Digitization Process
The following step outlines the process from a previous effort. The shoreline derived from 1970s aerial images was digitized in a previous project sponsored by the National Oceanic and Atmospheric Administration (NOAA) through the Coastal Zone Management Division at Puerto Rico Natural Resources Department (DRNA) (Contract Number 2015-000101 Assessment of beach morphology at Puerto Rico Island). The images were purchased from the Puerto Rico Highways & Transportation Authority Photogrammetry Office.
Aerial photos taken from 1964 to 1977 were used to create the shoreline of Puerto Rico for 1970s period. The approximate percentage of shoreline extracted by date was the following--> 1977 (56% approx.), 1973 (10%), 1971 (33% approx.), and 1964 (1%). Therefore, most of the shoreline was extracted from 1977 and 1971.
The digitization process was divided into four main sections: PR northeast, PR northwest, PR-southwest, and PR-southeast.
In ArcPro, a new file geodatabase was created, followed by a feature dataset. In the feature dataset, an empty line feature class was created for digitizing the shoreline. The aerial photo was digitized at the 1:1000 scale. The digitization began at the extreme southeastern point of the photo, moving counterclockwise towards the northwestern point.
The principal objective of the digitization exercise was to identify and draw the wet/dry line; the instantaneous water line on the aerial photo was used as a reference. Following shoreline definitions developed by Boak and Turner (2005), the next seaward line after the instantaneous water line was identified as the “groundwater exit point”, and the second line was identified as the “wet/dry line”. The priority was to identify and draw the wet/dry line; when that line was not visible, a groundwater exit point was drawn. In some cases, mainly located on the south coast of the Island, it was hard to identify the wet/dry line due to the brightness of the image and/or the coastal geomorphic configuration. The main reasons for insufficient visibility in aerial photos were the shadows, trees, and brightness in the image. Additionally, problems with poor raster resolution, overlapping of images that did not always align, and difficulty in identifying the wet/dry or groundwater line. Also, geometrically corrected images from the 1970s did not always align with orthophotos of 2010.

The scheme of the 1970s shoreline, from now on referred to as the "1970s NOAA shoreline," was standardized to match the new scheme created for the present project: "Shoreline mapping, change estimation and forecasting for the coast of Puerto Rico impacted by Hurricanes Irma and Maria."
The 1970s NOAA shoreline classification scheme was reclassified to match the current project scheme. An ArcGIS Pro Python Notebook and a stand-alone script in Python 2.5 were used to streamline the process.
This previous classification was reclassified using the subtypes and domains in this project: None--> NO VISIBILITY Non-Identified--> NO VISIBILITY, OTHER Rocky Coast--> ROCKY, BARE LAND River Mouth--> NO VISIBILITY Vegetation--> VEGETATION, Man-Made Structure--> ANTHROPOGENIC Wet/Dry Line--> BEACH, WET/DRY LINE OR RUN UP MAXIMA Groundwater Exit Point--> BEACH, GROUNDWATER EXIT POINT Eolianite--> ROCKY, BARE LAND Beach Rock--> ROCKY, BARE LAND
After the shoreline was reclassified to this new scheme, topology rules were run to correct errors. This feature polyline was corrected to avoid overlapping of the lines, repeated features or intersections. However, this feature polyline is not a continuous line. Gaps can be found along the line.

The geodatabase was transferred to USGS for final processing steps. The geodatabase feature class was exported as a shapefile (ArcToolbox >> Conversion >> To Shapefile >> Feature Class to Shapefile (multiple)), ensuring that the "Transfer field domain descriptions" was checked in the Environment Settings.
A YEAR field was added and calculated based on the IMG_DATE field so shorelines could be easily grouped by year.
Finally, the shapefile was projected (ArcToolbox >> Data Management >> Projections and Transformations >> Project) to WGS 1984 using the Puerto_Rico_To_NAD_1983 + Puerto_Rico_to_WGS_1984_4 geographic transformation.