Reclassifying tutorial

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  • In the processing toolbox window, search for the SAGA tool called ‘Reclassify grid values’, and then double click on it from the selection of tools.
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  • In the ‘reclassifying grid values’ window, select the IDW_500m grid raster. For the ‘Method’ option, select ‘simple table’ as this method allows you to input a range of values for a given field. For the ‘Lookup Table’ click on the button to the right of “Fixed Table 3x3’.
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  • The As concentration data for the 25 points were classified into 6 fields using a Jenks Natural Breaks Optimization method in another program prior to starting this tutorial (out of the scope of this tutorial). If you are using data which is different from the data used in this tutorial, you will need to decide on how best to classify your data in terms of data ranges. In the Fixed Table window, you have the option of adding or removing as many rows as you like. For this tutorial we are going to assign 6 rows with the following values (see image) for the minimum, maximum and new values. Then click ok.
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  • Keep the remainder of the inputs in the ‘Reclassify grid values’ window at their default settings, and assign a filename of ‘IDW_500m_Reclass’ for the output ‘reclassified grid’. Also make sure to check the box which opens the output file after running the algorithm. Then click run. The new reclassified grid will then appear in the map window as a greyscale raster surface.
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