calculate are of steep slop with in a polygon

[RandallClark1]

Hi guys,

So one thing i am encountering in my work is we end up doing a lot of slope analysis. I have that part down pretty well.

But what i would i like to do next is calculate the area of slope with in the a range that can be found with in our project area, ie 345 ac of slope between 15-20 percent,
50 acres of slope between 20-25, etc, or even just say "x acres of slope greater the 15 percent" and this is where i a running it a wall.

I have played around with spatial analysis tools but have not came up with anything. Can some one please point me in the right direction.

Thanks

[JeffreySwain]

After your slope analysis is done, you can then use the Extract by Values to pull out just the values within your desired range.  The new raster created could be analyzed to determine how many pixels are contained and therefore the area covered for each setting.  Also you could use the reclassify tool to divide the ranges into certain values, so the 15 to 20 % in one class, 21 to 40% in another and so on.  That raster would have the number of pixels in each range.

[EricRice]

Randall,

I think the first thing to clear up is whether or not the entire slope raster is the project area, or if you have some sort of polygon that represents a portion of the slope raster that is the definition of your project area.  I think you have a polygon that is a subset of the slope raster based on the title of your post.

If the entire slope raster is the project area, you need to Reclassify the raster first because slope rasters are float and you need an integer dataset.  Once you have a reclassified slope raster, input it into the Zonal Geometry as Table tool.

If you have a polygon representing the project area, run the Zonal Histogram tool on the slope raster (using the classified renderer with the correct ranges per class) using your polygon as the Zone features.  This tool will show the distribution (counts) for each class within each zone.  If you only have 1 zone (polygon) the results are very easy to interpret.  Counts can directly be converted to area by multiplying by the area of a single pixel and using some unit conversion factor to get whatever output units you want.

Regards,
Eric