dca.uw

raster to polygon producing blocky results

Discussion created by dca.uw on Nov 17, 2017
Latest reply on Nov 17, 2017 by Dan_Patterson

Short(er) version of the question: I have a raster surface (decimal values) that I want to convert into 5 categories of polygons based on class breaks, and the output must be smooth and visually appealing. Using the "contour list" tool and line smoothing (PAEK method), I'm able to produce nice contour lines that are basically what I want, but I need polygons. Back in the raster world, using reclass (to convert to integer) and then "raster to polygon", I get a jumble of sliver polygons and ugly blocky edges. I could smooth these out, but it also doesn't create concentric rings in places where it increases sharply, so I get non-consecutive values adjacent to each other. The screenshot below shows what it looks like when I use raster to polygon without simplification, and the simplified version is an even worse mess. The nice contour lines are drawn over it. How can I get polygons that look like what I see with these contour lines? 

Contours are what I'd like, but the raster-to-polygon is blocky

 

Long(er) version of the question: My input is a raster surface (double), and I want to produce polygons as output for 5 classes based on thresholds. I have ArcGIS Desktop and access to all the extensions. Although I may be a data nerd who doesn't see any problem with blocky edges and sliver polygons, my marching orders were to produce nice, clean polygons that show the larger trends in the data and remove the micro-fluctuations in the data. In other words, it needs to be smooth and visually appealing, and I have creative license to get there.

 

The raster is an air quality model, so it's not a conventional DEM terrain surface. There are massive fluctuations in the surface (Z) value in a very short distance, so contours will be very close to each other, but I do need them to be concentric, even if they are very narrow bands (like the contour lines above). I have already smoothed it and reduced the cell size to get this far. I suppose I could continue to smooth and resample until my raster data processing produces something similar to the contours. That said, I feel like I have what I want with the contours (visually), but I need polygons, not lines.

 

I found an Esri help doc on converting contours to polygons saying to rasterize it and then run raster to polygon. This doesn't exactly fill me with confidence, since that is the process I'm fighting with already! Is there some contouring tool that will do what I have above, but with the lines filled in as polygons?

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