Topographic Position Index derived from 1" SRTM DEM-S

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Topographic Position Index derived from 1" SRTM DEM-S

Topographic Position Index (TPI) is a topographic position classification identifying upper, middle and lower parts of the landscape. This dataset includes a mask that identifies where topographic position cannot be reliably derived in low relief areas. The TPI product was derived from Smoothed Digital Elevation Model (DEM-S; ANZCW0703014016), whi... more

Environmental Management Land Capability and Soil Degradation Landscape Ecology Natural Resource Management Soil Sciences not elsewhere classified

11 Feb 2000

22 Feb 2000

CSIRO Enquiries
1300 363 400

Topographic Position Index LAND Topography Models ECOLOGY Landscape TERN_Soils Land Surface Australia



Source data 1. 1 arc-second SRTM-derived Smoothed Digital Elevation Model (DEM-S; ANZCW0703014016). 2. 1 arc-second slope relief product 3. 3 arc-second resolution SRTM water body and ocean mask datasets. Topographic position index calculation TPI is a measure of topographic position, classified into three classes corresponding to upper slopes, mid-slopes and lower slopes. The method follows that of the "Drainage Channels Class" section of Warner, Cress and Sayre (2008) which is based on the TPI method of Jenness (2006) and Weiss (2001). The TPI classification uses relative elevation as a fraction of local relief; where the relative elevation is high compared to the local relief the class is upper slope, and where the relative elevation is low compared to local relief the class is lower slope. Intermediate values are classified as mid-slopes. This use of residuals compared to a smoothed elevation model to produce relative elevations is similar to the method described by McRae (1992). Relative elevation is the difference between local (cell) elevation and the mean elevation over a 300 m radius circle (approximately: the calculation actually uses 10 grid cells at 1 arc-second resolution). Local relief is calculated as the standard deviation of elevation over the same circular region. The classification is: TPI = 1 if relative_elevation < -0.5 * local relief (lower slopes) 3 if relative_elevation > 0.5 * local relief (upper slopes) 2 otherwise (mid slopes) In relatively flat areas the finite accuracy of a DEM limits its ability to discriminate topographic position. The mask included with the TPI layer identifies areas that are too flat to reliably identify upper, middle and lower landscape positions. It is based on the 'Slope-Relief' classification and the TPI mask has values of 1 where there is sufficient relief for TPI to be meaningful and 0 where TPI should not be used. The TPI calculation was performed on 1° x 1° tiles, with overlaps to ensure correct values at tile edges. The 3” arc-resolution version was generated from the 1” TPI class and mask products. This was done by aggregating the 1” data over a 3 x 3 grid cell window and taking the mean of the nine values that contributed to each 3” output grid cell. The result was then converted to integer format, avoiding truncation errors and ensuring that (for example) values between 1.5 and 2 were assigned to class 2, and values between 2.5 and 3 were assigned to class 3. The 3” TPI and TPI mask data were then masked using the SRTM 3” ocean and water body datasets.

Access to this data has been made possible by the Terrestrial Ecosystem Research Network (TERN), supported by the Australian Government through the National Collaborative Research Infrastructure Strategy and the Super Science Initiative.

Creative Commons Attribution 4.0 International Licence

CSIRO (Australia)

Gallant, John; Austin, Jenet (2012): Topographic Position Index derived from 1" SRTM DEM-S. v6. CSIRO. Data Collection.

All Rights (including copyright) CSIRO 2012.

The metadata and files (if any) are available to the public.

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Location Details

10°0′0″ S

44°0′0″ S

154°0′0″ E

113°0′0″ E


More about this Collection

John Gallant

Terrain Analysis Research Scientist

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About this Project

1181.2 TERN Facility No9 InfoGrid GRUNDY

The Soil and Landscape Grid of Australia is a comprehensive fine spatial resolution grid of functional soil attributes and key landscape features across Australia. The landscape attributes are derived from the data collected by the Shuttle Radar Topography Mission, whilst the soil attribute surfaces are modelled from existing soils information. The... more

John Gallant

National Elevation and Terrain Datasets

SRTM-derived elevation and terrain covariate datasets at 1 second or 3 second resolution


John Gallant

Jenet Austin

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