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I am not so familiar with 'interpolation' math, albeit I grasp the underlying logic. I was wondering if there is a rule of thumb in the choice of the number of neighbor points to use in IDW interpolation method. This site (http://www.quantdec.com/SYSEN597/GTKAV/section9/chapter_29b.htm) provides a good description of the method, and of the difference between a fixed search radius or a variable one (the latter depending on the specified number of neighbors). But I am still wondering on what basis the number of neighbors has to be chosen. Does it somehow depend on the number of original data points? By the way, I use arcGIS 10.1. w/ advanced license.

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You should read help for the function in ArcGIS here. However, you could define number of neighbor points (cells) and the function will take the exact number of nearest points. Or you could define search radius in i. e. meters and all the points (cells) that fit into this radius will be taken into the interpolation.

To choose the amount of neighbours, it depends of type of input data. If you choose many neighbours i.e. for interpolating DEM, the result will be more smooth than if you choose less. Otherway, if you will choose many neighbours, the result will have bigger deviation compare to interpolation with less neighbours. Other example, if you have some meteostations as a points and there is one that doesn'n have data and you want to interpolate it using IDW, imagine the influence of input neighbours. This IDW method strongly depends on spatial resolution of data. What kind of data do you have?

  • I believe the question was how to decide the amount of neighbours with mathematical reasoning (@NewAtGis, correct me here if I'm wrong), not where to enter the value in the GUI. Maybe you can elaborate on your answer to include that too? – Martin Jul 16 '15 at 9:22
  • Yes, @Martin is correct in pointing out that I was wondering how to decide how many neighbors can reasonably be chosen. Thank you. – NewAtGis Jul 16 '15 at 9:25
  • To choose the amount of neighbours, it depends of type of input data. If you choose many neighbours i.e. for interpolating DEM, the result will be more smooth than if you choose less. Otherway, if you will choose many neighbours, the result will have bigger deviation compare to interpolation with less neighbours. Other example, if you have some meteostations as a points and there is one that doesn'n have data and you want to interpolate it using IDW, imagine the influence of input neighbours. This IDW method strongly depends on spatial resolution of data. What kind of data do you have? – david_p Jul 16 '15 at 9:30
  • @david_p, please include the above comment as an edit in your answer. NewAtGis, maybe you can post a screenshot (with scalebar or similar) of your data so we can have an actual case to discuss? – Martin Jul 16 '15 at 9:44
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    Like as Martin said, you should try IDW interpolation with different options and see how the data behave. Also you can try other interpolation methods in ArcGIS, like Spline or Natural Neighbours. Here is explanation how interpolation methods in ArcGIS works (resources.arcgis.com/en/help/main/10.1/index.html#/…). However interpolation is strongly subjective theme, so you should know what result do you expect and set interpolation method upon this expectation. – david_p Jul 16 '15 at 11:46

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