GEOGRAPHY & CARTOGRAPHY CALCULATOR
Topographic Position Index
A precise tool.
What is the Topographic Position Index & How does it work?
The Topographic Position Index (TPI) quantifies how a specific location sits relative to its surrounding terrain. By comparing the elevation of a target cell to the average elevation of its neighbourhood, TPI highlights whether the point is on a ridge, in a valley, or on a flat surface.
Mathematically, TPI is expressed as the difference between the cell’s elevation (z_i) and the mean elevation of all cells within a defined radius ((bar{z}_{N(i)})). Positive values indicate higher-than‑average positions (ridges), negative values indicate lower‑than‑average positions (valleys), and values near zero suggest flat or gently rolling terrain.
Because TPI is scale‑dependent, the choice of neighbourhood radius directly influences the features that are emphasized. Small radii capture micro‑topography such as individual bumps, while larger radii reveal broader landform patterns like mountain ranges or basin structures.
TPI = z_i – \bar{z}_{N(i)}
TPI = Topographic Position Index, z_i = elevation of the target cell, \bar{z}_{N(i)} = mean elevation of the neighbourhood cells.
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Result
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Frequently Asked Questions
What does TPI stand for?
TPI stands for Topographic Position Index, which measures how a point sits relative to its surrounding terrain.
How is TPI calculated?
TPI is calculated by subtracting the mean elevation of neighboring cells from the elevation of the target cell.
What do positive and negative TPI values indicate?
Positive TPI indicates a location higher than average, while negative TPI indicates a location lower than average.
Why is the radius important in TPI calculation?
The radius defines the neighborhood of cells used to calculate the mean elevation, affecting how TPI reflects local terrain features.
Can TPI be used for any type of terrain?
Yes, TPI can be applied to various terrains, including mountains, plains, and valleys, to analyze their topographic characteristics.
How does TPI differ from other elevation metrics?
Unlike simple elevation measurements, TPI provides a relative position within the landscape, highlighting local highs and lows.
What are some applications of TPI in geography?
TPI is used in hydrology to identify drainage patterns, in ecology to study habitat suitability, and in urban planning for infrastructure development.
Results are for informational purposes only and do not constitute professional advice.