I have recently encountered the Pick tool in the Spatial Analyst of ArcGIS. I understand what the tool does; it creates an output raster using a list of input rasters and a 'position' raster which dictates for each grid cell in the output which input it should receive the value from. I've looked for questions on GIS.SE that mention the Pick tool and there don't seem to be any. Having used GIS for quite some time now, I can't think of a past scenario when this operation would have been useful to me. Even the ArcGIS help documentation, which is normally quite extensive, doesn't reveal a use-case for the tool. I'm very curious whether any of you have ever used this tool and if so what for? Is there some niche area that I am overlooking, e.g. some operation involving multi-spectral images, in which this is a common operation?
Pick is the map algebra analog of a "case" or "switch" statement. Like them it is not indispensable but it can be convenient (and more efficient than deeply nested binary logical operators).
Notable among the uses to which I have put this operation is its ability to implement a cellular automaton.
Another handy use is random selection of rasters. A worked example appears on this site at Creating raster by randomly choosing cell value from multiple overlapping rasters?
most of the tool can be replaced with Map algebra, but the syntax of pick makes it easy to use.
I've used it for mosaicking with multiple masks (you have a set of classification, and you want to combine them based on geographical stratification.)
It is also quite usefull in combination of the local toolset. For example, one of those tools can find the position of the highest value in a set of raster. So if you add one to the result, you can pick the value after the maximum. This is quite usefull for time series analysis.