By Chelsea Scott & Chris Crosby
Topographic differencing measures landscape change from a variety of natural and anthropogenic processes including urban growth, flooding, coastal erosion, earthquakes, volcanic eruptions, and landslides. Interest in differencing continues to grow as more areas are covered by multi-temporal topography datasets (i.e., two or more topography datasets at the same location), thanks in part to efforts to collect national-scale data like the US Geological Survey’s 3D Elevation Program (3DEP). However, differencing results must be interpreted with care to ensure that sources of noise are not confused with real signals of landscape change.
Vertical differencing is the subtraction of grid-based digital elevation models (DEMs). Because topographic differencing quantifies changes to the landscape that are often of a similar magnitude to the errors in the source topography data, topographic differencing tends to accentuate errors in the input datasets. Below, we discuss four examples of common errors in vertical topographic differencing, illustrating cases where the apparent change largely reflects noise and not true landscape change.
Interested in learning more about topographic differencing? See our topographic differencing resources with video tutorials, blog posts with differencing examples, workshop presentations, links to GitHub code repositories, and a differencing exercise designed for undergraduate courses.