Area method compared with Transect method to measure shoreline movement

Abstract

Vector GIS represents shorelines as polylines that show the boundaries between land and water. This article compares two methods to measure how boundaries move among time points. The Area method converts the polylines at various time points into polygons of either land or water. The Area method measures temporal change as loss or gain of land areas. The Transect method requires subjective decisions to draw a baseline near the shorelines and then to draw transects that emanate from the baseline to intersect the shorelines. The Transect method measures temporal change as the distance between the intersection points along each transect as in the software packages AMBUR and DSAS. This article compares the conceptual foundations of the two methods. We illustrate how the Area method produces results for cases where the Transect method encounters practical difficulties. We list each method’s characteristics, so researchers can align the method with their research question.

Keywords:

• AMBUR
• boundary movement
• coastal studies
• DSAS
• GIS
• shoreline change

Acknowledgement

The United States National Science Foundation supported this work via the Long Term Ecological Research (LTER) network’s Plum Island Ecosystems grant OEC-1637630. The Edna Bailey Sussman Trust provided additional funding via a grant entitled “Mapping marsh dynamics in coastal ecosystems”. Christine Burns created the data, which the Georgia Coastal Ecosystems LTER site posted at gce-lter.marsci.uga.edu/data/GIS-GCET-1810.

Authors’ contributions

Sam Khallaghi developed the conception, conducted the analysis, drafted the article, and interpreted the results. Robert Gilmore Pontius Jr contributed important intellectual content concerning conception, interpretation, and revision.

Computer code availability

We did not write code for this manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Software and data availability

The Applied Coastal Research Laboratory at Georgia Southern University produced a package for the R environment called Analyzing Moving Boundaries Using R (AMBUR) available at http://ambur.r-forge.r-project.org/. Our article uses the open-source AMBUR software to demonstrate the Transect method. The United States Geological Survey produced the Digital Shoreline Analysis System (DSAS), which is freely available at https://www.usgs.gov/centers/whcmsc/science/digital-shoreline-analysis-system-dsas?qt-science_center_objects=0#qt-science_center_objects. DSAS also performs the Transect method. The Area method consists of a few basic steps that various open-source GIS packages can perform. Data are at https://pie-lter.ecosystems.mbl.edu/data.