Baseline & Transect method compared to Polygon Overlay method to measure boundary change

Authors: Sam Khallaghi*, Clark University
Topics: Geographic Information Science and Systems, Coastal and Marine, Remote Sensing
Keywords: Coastal; Comparison; GIS, Polyline; space-time; temporal change
Session Type: Guided Poster
Day: 4/6/2019
Start / End Time: 8:00 AM / 9:40 AM
Room: Roosevelt 3.5, Marriott, Exhibition Level
Presentation File: No File Uploaded


Vector GIS represents shorelines as polylines that separate land from water. Such boundaries tend to move over time, and it is not immediately clear how to characterize the spatio-temporal change during sequential time intervals, especially when the boundary lengths vary among the time points. One approach to measure shoreline change is the Baseline & Transect method, which requires the user to draw a baseline polyline along one side of the shorelines and then to draw transects that emanate perpendicular to the baseline. Computation requires that each transect intersect the shoreline at each time point exactly once, which creates conceptual challenges with highly curved shorelines. The Baseline & Transect method measures rate of change based on the distance between intersection points on each transect. I compare the Baseline & Transect method to a Polygon Overlay method, which converts the boundary polylines at each time point into polygons, where each polygon is either water or land. Then a map overlay of the time points forms new polygons of combinations of land’s loss or gain during sequential time intervals. The comparison reveals that the Baseline & Transect reports movement distances, requires subjective decisions and is impossible to implement for some boundaries. In contrast, the Polygon Overlay method reports change areas, does not require subjective decisions and always produces interpretable results for coherent polygons.

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