topic Calculating slope in ArcGIS Spatial Analyst Questions

Calculating slope

MarinaMeter — Thu, 23 Jun 2016 17:37:13 GMT

I have to calculate a percentage of slope from an Idaho 30m DEM in ArcMap. My work asked me to calculate a 2-8% slope and an >8% slope. I do not want to mess this up so im asking for advice. I have a projection of NAD_83_Idaho_TM (meters) - I have used the slope tool to calculate percent rise and values are from 0-80. What am i doing wrong here? Any suggestions would be helpful

Thank you Kindly

Re: Calculating slope

DarrenWiens2 — Thu, 23 Jun 2016 17:40:31 GMT

Now just use Reclassify to get your classes <2, 2-8, and >8 (or one of the classes, or a combination). The units of your slope output are %.

Re: Calculating slope

MarinaMeter — Thu, 23 Jun 2016 17:46:36 GMT

with the values 0-80 i was confused, why not 0-100%? I guess that is where im stuck, also should i use the relcass tool, or classify in the symbology with 3 classes, how do i do this (natural jenks)? Eventually I will need to export these into separate files

Re: Calculating slope

DarrenWiens2 — Thu, 23 Jun 2016 17:53:27 GMT

It depends what your actual requirements are. If you want a new raster layer containing the original values (say, between 2-8%), use the Con tool or raster calculator expression like: Con(("YOUR_RASTER_LAYER" < 😎 & ("YOUR_RASTER_LAYER">2),"YOUR_RASTER_LAYER")

Using Reclassify, you could make a new raster with values 1, 2, 3 to correspond to classes <2, 2-8, >8.

Your values only go to 80%, because that's the max slope value (presumably).