Tuesday, 20 March 2018

spatial analyst - Using Combine tool in ArcGIS Desktop?



I have two raster layers. Layer A has a cell size of 1020 m. There are 31,840 rows in the attribute table, each corresponding to a different 1020 m x 1020m cell. Layer B has a cell size of 30 m. The attribute table associated with this only has two entries - value (0,1) and count of value.



I want to combine the two layers such that I have the ID of the 1020 m x 1020 m cell from layer A that spatially overlaps the values from layer B. After reading How to find the area of raster values within polygon zones? I used the "combine" tool. But the number of rows in the output are not what I would expect. Instead of the new layer having the same number of rows as layer A (31,840), there are considerably fewer (only ~22,000). The graphic below shows an example - two similar areas with roughly the same amount of missing data in layerB. An output from the Combine tool was produced for one of these areas, but not for the other! I don't understand what could have gone wrong! Any ideas?


Left: two areas with similar amounts of missing data. Right: Only one of the two areas got a result from the Combine tool.




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