topic Re: Slope and polygon editing in ArcGIS Spatial Analyst Questions

Slope and polygon editing

NicoleDarnell — Thu, 02 Feb 2012 15:11:46 GMT

I have a pretty simple question. My task is to calculate slope and eliminate all slopes over 30% from a set of existing polygons. I can create the slope, classify it to only display the slope over 30% but have no idea how to convert the raster to a polygon in order to clip it from the existing set of polygons. I *think* my problem is that I cannot figure out the conversion of the slope file to polygon. I thought it wouldn't convert because it is a floating point, but when I tried to convert to integer, I seem to have lost my slope information. I feel like this is very easy, yet just beyond my grasp.

Thanks in advance.

Nicole Darnell
Archaeologist / GIS Specialist
Dominguez Archaeological Research Group

Re: Slope and polygon editing

DanPatterson_Retired — Thu, 02 Feb 2012 15:33:41 GMT

Do you just want a map your map converts slopes > 30% to null and the rest to some other value? If so, then check the SetNull tool in the Spatial Analyst toolset. You can't convert a floating point grid to a polygon shapefile, so you will have to specify what you want as output.

Re: Slope and polygon editing

NicoleDarnell — Thu, 02 Feb 2012 15:53:38 GMT

What I want is a shapefile that I can use to clip the data over 30% from the existing polygon. Our polygon represents our survey area and we need eliminate slopes over 30% because we are not obligated to survey said areas. If I ended up with a polygon that had all of the percentages of slopes, I figure I can just export those over 30% and use the result to clip my survey area. I just can't get the initial polygon that gives me the percentage slope. I hope this makes sense.

Re: Slope and polygon editing

NicoleDarnell — Thu, 02 Feb 2012 15:55:13 GMT

I know that I can display the data I have and that is okay, but what I really need is to be able to calculate the acreage we surveyed outside of the 30% grade/slope range. So, really I need more than just a map...

Re: Slope and polygon editing

DarrenWiens2 — Thu, 02 Feb 2012 16:54:44 GMT

1.) As Dan said, use the SetNull tool to filter out those pixels with slope > 30
2.) Convert the raster with only slopes < 30 to a polygon feature class with the Raster to Polygon tool

Re: Slope and polygon editing

NicoleDarnell — Thu, 02 Feb 2012 17:37:33 GMT

Ah ha. I get it. Thank you both so much. Finally, success!

Re: Slope and polygon editing

MirjaSchulz — Thu, 23 Feb 2012 17:38:05 GMT

i have nearly the same problem. my task is to calculate slope and eliminate all slopes >1.5° from a set of existing polygons. i can create the slope and classify it with the raster calculator (0=>1.5 and 1=<1.5) but i don`t know how to convert the raster to a polygon which i can clip/erase from the existing set of polygons.