What is the Digital Shoreline Analysis System (DSAS)?
DSAS is a free, USGS-built application, described by USGS as a “standalone application that calculates shoreline or boundary change over time” and used alongside a geographic information system (GIS). It is the standard tool for measuring coastal change in the United States and underpins the USGS National Assessment of Shoreline Change. The current release, version 6.2, came out in October 2026.
How does DSAS measure shoreline change?
You give DSAS a set of historical shorelines (each dated, digitized from maps, aerial photos, lidar, or satellite imagery) and a reference baseline running parallel to the coast. DSAS then generates transects — measurement lines cast perpendicular to the baseline at a spacing you choose — and measures the distance from the baseline to each shoreline where the transect crosses it. Combining those distances with each shoreline's date and positional uncertainty produces the change statistics.
DSAS lays a comb of lines across the coast, measures where the shoreline sat on that line in each year, and turns the spread of those positions into a rate of change per transect.
What do EPR, LRR, NSM and SCE mean?
DSAS reports several statistics per transect. The two you will see most are the rates — EPR and LRR:
| Stat | Name | What it is |
|---|---|---|
| EPR | End Point Rate | Net change between only the oldest and newest shorelines, divided by the years between them — an annualized rate. Used for short-term change. |
| LRR | Linear Regression Rate | The slope of a least-squares line fit through every dated shoreline on the transect. Uses all the data; needs at least three shorelines. Used for long-term change. |
| NSM | Net Shoreline Movement | The raw distance between the oldest and youngest shoreline (the number EPR annualizes). |
| SCE | Shoreline Change Envelope | The total distance between the shoreline farthest landward and the one farthest seaward across all dates. |
Across all of these, the sign convention is consistent: negative = erosion, positive = accretion.
DSAS definition and metric list: USGS, Digital Shoreline Analysis System (DSAS) (updated Aug 6, 2026; v6.2 released Oct 2026). EPR / LRR / NSM definitions and the erosion-negative convention: USGS Open-File Report 2012-1008 (National Assessment of Shoreline Change methods) and the DSAS v5.1 user guide, USGS Open-File Report 2021-1091.
EPR vs LRR: which rate should I trust?
They answer different questions. EPR uses just two shorelines, so it is simple and captures the most recent trend — but a single stormy or calm end-year can skew it. LRR uses every shoreline, so it is more robust to any one bad year and better describes the long-term behavior of a coast. USGS typically applies LRR to long-term change (on the order of ~100 years) and EPR to short-term change (on the order of ~30 years). If only two shorelines exist, DSAS can compute only an EPR.
Why does the shoreline change rate matter for my property?
A FEMA flood zone and Base Flood Elevation describe flood height; a DSAS rate describes whether the land itself is moving away. A home can sit comfortably above its BFE and still be on a beach retreating several feet a year — the shoreline, not the water level, is the clock. Psammite builds its coastal readings on this USGS DSAS record. See it in action on the New York South Shore map (3,518 transects) and the California coast.
What is the erosion rate at your address?
A parcel screening returns the USGS DSAS long-term change rate for the shoreline in front of your property, plus setback, FEMA zone, and storm-surge exposure.
Check your address · $99Frequently asked questions
What does DSAS stand for?
DSAS stands for Digital Shoreline Analysis System, a software tool built by the U.S. Geological Survey to calculate shoreline change over time.
What is a shoreline change rate?
It is the speed at which a shoreline is moving, expressed in feet or meters per year. A negative rate means erosion (land loss); a positive rate means accretion (land gain).
What is the difference between EPR and LRR?
EPR (End Point Rate) uses only the oldest and newest shorelines. LRR (Linear Regression Rate) fits a line through all available shorelines, so it is more robust and is used for long-term rates.
Does a negative rate mean erosion?
Yes. In DSAS output, negative values indicate erosion and positive values indicate accretion.
DSAS rates on 3,518 South Shore transects.
Montauk, Westhampton, Sagaponack & more — per-beach DSAS rates.
Bluff retreat and shoreline change on the Pacific edge.
Flood height vs the moving shoreline — two different clocks.
The flood-zone half of the picture.