Creating IDW and Spline Interpolation Maps Using QGIS

Performing IDW, Kriging and Spline Interpolation Methods Using QGIS (and GRASS plugins)

Purpose

The purpose of this tutorial is to look at tools and specific plugins in Quantum GIS (QGIS), which will allow for the Interpolation of a sampled dataset of points, in order to create interpolation maps. The interpolation methods that are going to be investigated include: Inverse Distance Weight (IDW), Kriging and Splines.

Data

The data set being investigated for the purpose of this tutorial is a lake water geochemical dataset, consisting of 25 sampled locations on Frame Lake (Yellowknife, North West Territories), provided by the Patterson Research Group at Carleton University. This dataset has measured concentrations of major chemical elements (in PPM) and trace elements (PPM and PPB). The purpose of collecting this data is to map the concentration distributions of harmful elements, such as As, Pb, Hg and Cr within the lake, in order to determine which parts of the lake need the most remediation work done before trying to reintroduce fish populations into the lake.

This is unpublished data, and therefore it cannot be shared yet. However, any point data-set can be used for the purpose of this tutorial, so long as the points have a geographic location and an attribute that can be used for the interpolation (elevation, chemical concentration, etc). Some good sources of data for this tutorial include: Geobase, Geogratis, GIS Data Depot and Free GIS Data