topic Polygon density in ArcGIS Spatial Analyst Questions

Polygon density

MatejTacer — Thu, 25 Aug 2011 07:06:18 GMT

Hi,
I need to overlap a grid over the polygon layer and calculate the sum of polygon areas for each cell. The output should be a raster layer. So, I have only polygon layer and need to create raster showing sum of areas in each cell.
The problem is similar to LineDensity tool for lines, but I can't find the appropriate tool for polygons.

Thanks for your suggestions,

Re: Polygon density

BruceNielsen — Thu, 25 Aug 2011 18:04:29 GMT

If you want to try a vector-only approach, you could use the Generate Fishnet tool to create your grid, the Intersect tool to find the relationship between your polygons and grid cells, then Summarize to find the area of the polygons that touch each grid cell.

Re: Polygon density

MatejTacer — Fri, 26 Aug 2011 05:40:11 GMT

Thank you, Bruce!
That's what I've resorted to:
I created grid using python and osgeo.ogr, union and area calculation are yet to be done. Python comes in handy since I need to do it for 1000+ layers.
BTW, not sure if I understand that Dodt's opinion of Python - sounds like criticism. If that's so, I strongly dissagree :-))

Best,

Re: Polygon density

BruceNielsen — Fri, 26 Aug 2011 10:59:31 GMT

BTW, not sure if I understand that Dodt's opinion of Python - sounds like criticism. If that's so, I strongly dissagree :-))

Best,

Believe me, it's not a criticism. He's making the point that Python is far superior to BASIC (and a lot of other languages IMHO) by orders of magnitude. To fully appreciate Optimus Prime's abilities relative to those of a pickup, view one of the Transformers movies.

Re: Polygon density

JeffreySwain — Mon, 29 Aug 2011 10:40:54 GMT

Not to break up the Transformer party, but perhaps the zonal tools may yield an answer. Dare I say, "they are more than meets the eye."

I am not sure what you mean by "sum of polygon areas for each cell." The Zonal tools can generate a raster output based on a 'zone' or polygon/raster, but to find the number of polygons per cell makes me think you have a rather larger cell for the raster or tiny polygons. Based on what I think you mean, I would recommend the Zonal Statistics and choose "sum."