TRI: Putting a Number on How Rugged the Terrain Is
Some ground is billiard-table smooth; some is a chaos of gullies and crags. The Terrain Ruggedness Index compresses that difference into a single value by measuring how much elevation jumps around each pixel.
How it reads the surface
TRI sums the elevation differences between a cell and its neighbours (Riley's formulation uses the square root of the summed squared differences). Level ground scores near zero; broken, dissected terrain scores high. It quantifies local heterogeneity rather than steepness itself.
The math behind it
How to interpret the output
Near 0 = level ground · increasing values = progressively more rugged, dissected terrain.
The data it needs
| Derived from | Digital Elevation Model (SRTM / Copernicus, 30 m) — not an optical band index. |
Real-world use
It is applied in wildlife-habitat modelling (ruggedness as refuge or barrier), military and access analysis, and geomorphological characterisation.
Watch out for
TRI cannot tell true roughness from DEM noise, and like TPI it depends on window size — a jittery DEM will read as "rugged". Smooth or quality-check the DEM first if ruggedness is your headline result.
Compute TRI on your own study area
Skip the code. Draw or upload a boundary and Spatial Research Suite runs TRI on live data — with cloud masking, exports and citations built in.
Run this analysis in GISforus →Frequently asked
What is the difference between TRI and slope?
Slope measures the overall gradient; TRI measures local variability — how much neighbouring elevations differ — so a uniform steep slope can be steep but not rugged.
Does DEM noise inflate TRI?
Yes — random elevation error reads as roughness, so noisy DEMs overstate ruggedness; clean the data first.