topic Re: Find percentage of raster classes inside polygon in ArcGIS Spatial Analyst Questions

Find percentage of raster classes inside polygon

AdamBorczyk — Sun, 20 Aug 2017 00:37:26 GMT

I have a raster representing glacierized area with 2 classes: distinction between ice and snow. I also have DEM of the area. I would like to calculate an average height of the boundary between those two classes. I came up with an idea I could somehow calculate how many pixels of each class belong to a given height range (like 500-515m a.s.l.). For example (with a picture):

100% of snow in this range isn't what I'm looking for (it's not a boundary)
100% of ice neither
80% of ice and 20% snow is not a boundary (could be a snow patch)
40% of snow and 60% of ice probably is a boundary (values are arbitrary and I'd like to evaluate them)

So I reclassified DEM to 15m intervals and vectorized it. And now I have no clue. The Zonal Statistics tool only allows me to calculate statistics like MIN, MAX, MAJ etc., whereas I need a percentage - a custom equation. Or maybe there is a different way?

Re: Find percentage of raster classes inside polygon

JayantaPoddar — Sun, 20 Aug 2017 08:35:06 GMT

One way is to convert the classified Raster to Polygon (non-simplified). Then, use Tabulate Intersection.

Re: Find percentage of raster classes inside polygon

DanPatterson_Retired — Sun, 20 Aug 2017 09:36:39 GMT

Totally not tried, but this percentage question keeps cropping up, but I think a .... zonal sum / zonal count .... would give you the necessary ratio, if snow were classed as 1

zones - regiongroup your vectorized contour areas
classify ice and snow data
1. ice - class 0
2. snow - class 1
zonal area - is the Count column in the zonal statistics as table column
zonal sum - is the sum column in the zonal statistics as table column, sum option
do the math in a new field in the table, join back to the polygon zone

Re: Find percentage of raster classes inside polygon

AdamBorczyk — Thu, 24 Aug 2017 11:51:15 GMT

Thank you, that made it. Afterwards I only had to select by attributes (where X/Y > Z) and do some Joins and Spatial Joins to get a clean attribute table with glacier name and the value. In my case, where more than one "ranges" were selected I also also summarized them by original FID, so I got an average of all selected boundaries (ranges).

Re: Find percentage of raster classes inside polygon

TylerSchlachter — Tue, 02 Apr 2019 15:17:24 GMT

This is a great answer.

Almost all of the zonal statistics related approaches to this problem seem overly complicated.