topic Re: How to Find Slope for Polygon Feature in ArcGIS Pro Questions

How to Find Slope for Polygon Feature

GraceTortorici — Sun, 17 May 2020 20:48:46 GMT

Hi all! I have gathered SRTM data and from there gathered the slope for my desired region of study. I am specifically looking at tree growth and reforestation. I have a layer of polygons outlining the tree growth I want to specifically look at. How would I be able to find the slopes for these polygons? I know how to use the Extract Multi Values to Point tool, but these are polygons not points. I also tried the Zonal Statistics as Table tool, but it did not work. Any suggestions?

Re: How to Find Slope for Polygon Feature

DanPatterson — Mon, 18 May 2020 01:18:25 GMT

Zonal Statistics—Help | Documentation

and its tabular equivalent should work. What did you use and specify for the tools? Did you get errors or just unexpected results?

Re: How to Find Slope for Polygon Feature

GraceTortorici — Mon, 18 May 2020 02:47:05 GMT

Hi Dan,

I guess I am just confused on how to run the tool...I created two new fields in my polygon attribute table (one for DEM and one for slope). I do not know if this is right, but I don't see another way. This is my process. The output is generating an empty table. Treegrowth are all of my polygons. Hillshade_STRM_Clip_Clip is my DEM. I also tried this with my slope raster, and got the same results. Thanks!

Re: How to Find Slope for Polygon Feature

DavidPike — Mon, 18 May 2020 08:41:55 GMT

What's the resolution of the SRTM you're using? what's a typical size of your polygon area?

Your zonal statistics can take an average (and many other stats) of the raster cell centres which intersect your polygons.

Though it's highly unlikely that the slope will be regular across the polygon, or in the same direction, unless we are looking at vineyards or something?

Re: How to Find Slope for Polygon Feature

GraceTortorici — Mon, 18 May 2020 15:58:39 GMT

Hi! I am unsure on how to find the resolution, I am unable to see any information in the display properties. I downloaded a single SRTM tile from Earth Data. Most of my polygons have a shape area of 0...do not know why. Is that normal? They are measuring some decent size areas of tree growth.

Re: How to Find Slope for Polygon Feature

DavidPike — Mon, 18 May 2020 16:13:08 GMT

I would take a stab at your data not being projected. I believe Pro can do slope etc with a GCS nowadays but I'd say best practice is to project it if you want to play nice with other data.

Re: How to Find Slope for Polygon Feature

GraceTortorici — Mon, 18 May 2020 22:41:00 GMT

That worked!! Thank you so much Dave!!