topic Re: IDW Interpolation in ArcGIS Spatial Analyst Questions

IDW Interpolation

PatrickWard — Mon, 08 Nov 2010 22:30:21 GMT

I am trying to create a raster that interpolates weather station rainfall readings (point data) over areas in which there are no weather stations. When I use the IDW tool, there is an interpolation over the area defined by the northernmost, southernmost, easternmost, and westernmost weather stations, but I would actually like to extend the interpolation beyond these boundaries so that it can later be spatially joined with a polygon shapefile. Does anyone know if/how this can be accomplished?

Re: IDW Interpolation

DanPatterson_Retired — Mon, 08 Nov 2010 23:47:41 GMT

It would be horrendously easy to simply set the analysis extent to a larger size to extend to your desired boundary, but I would suggest that the results would be meaningless or misleading at best unless you know that such an interpolation would generate valid results beyond the bounds of the input data. Also, why have you picked IDW as the interpolator given the other options available to you. Perhaps there is a problem design issue that you could address before settling in on a means to fill in the gaps between stations.

Re: IDW Interpolation

toddsams — Tue, 09 Nov 2010 15:04:53 GMT

You may want to take a look at the PRISM datasets (if you have not already) http://www.prism.oregonstate.edu/products/matrix.phtml?view=data

Re: IDW Interpolation

JoanneDollasin — Tue, 05 Feb 2013 07:05:57 GMT

Hi! I'm Joanne & I'm a newbie in ArcGIS...
I guess my problem is somewhat related to this post....
Specifically, I have a rainfall map (Isohyets) measured in mm
(precipitation)... I wanted to
know a particular value (precipitation) in points between these
lines... how can I do this? Do I have to convert/interpolate these polylines
so I could have a Rainfall raster instead? So that I would know the
precipitation in any point based on cell values of the Rainfall raster? If so,
how do I make a raster map out of my rainfall contours/isohyets? By the way, I
have a DEM of 20-m resolution. Will this be of any help in
converting/interpolating my rainfall map? Pls help.
Thanks & best regards.

Re: IDW Interpolation

JoanneDollasin — Tue, 05 Feb 2013 07:30:47 GMT

It would be horrendously easy to simply set the analysis extent to a larger size to extend to your desired boundary, but I would suggest that the results would be meaningless or misleading at best unless you know that such an interpolation would generate valid results beyond the bounds of the input data. Also, why have you picked IDW as the interpolator given the other options available to you. Perhaps there is a problem design issue that you could address before settling in on a means to fill in the gaps between stations.