topic Re: Aspect to vectors/polygons in ArcGIS Spatial Analyst Questions

Aspect to vectors/polygons

LaszloKomaromi2 — Mon, 07 Nov 2016 12:34:10 GMT

Hi all,

I was wondering if you could help me out with a specific issue. I have an aspect map that I would like to convert into polygons based on aspect colours (directions). It is needed for my research in which I am separating two glaciers. Any idea how I should get around this task in ArcMap?

Thanks in advance.

Laszlo

Re: Aspect to vectors/polygons

DanPatterson_Retired — Mon, 07 Nov 2016 13:25:15 GMT

You will have to classify you raster to a nominal scale rather than using the actual aspect values. The symbology can be used to guide you. You can only save an integer grid to a polygon file, using the Conversion Tools to do this, but the reclassification step is needed.

I am also moving this thread to its rightful home https://community.esri.com/community/gis/analysis/spatial-analyst?sr=search&searchId=09e7e10f-de81-4bb7-af9a-df3668b95847&searchIndex=0‌ to facilitate getting proper comments

Re: Aspect to vectors/polygons

LaszloKomaromi2 — Mon, 07 Nov 2016 14:24:38 GMT

Many thanks for your reply Dan. That means I have to use the actual directions instead of values which is obvious, I am just not sure which feature to use for that. My glaciers divide along a Northeast and Southeast aspect divide which makes this task easier.

Re: Aspect to vectors/polygons

DanPatterson_Retired — Mon, 07 Nov 2016 14:41:44 GMT

The aspect raster is a floating point raster

http://desktop.arcgis.com/en/arcmap/latest/tools/spatial-analyst-toolbox/aspect.htm

you have to reclass it to an integer raster. BUT just taking the int of the layer is going to yield you want too many classes. So, 0-15 degrees... call it 1, 15-30, call it 2... or whatever. Then when you have it reclassed, you can convert that to a shapefile and reassociate the raw information summary with the polygons. Don't start doing averages unless you are familiar with directional statistics (I have a blog post on it)

Re: Aspect to vectors/polygons

LaszloKomaromi2 — Mon, 07 Nov 2016 14:50:20 GMT

That's great. I won't get started with averages. I don't think it is necessary as there is a clear divide between two opposing directions.For that reason I will simply classify the directions as N, NW, E, SE, S, SW, W, NW.

Thanks for your invaluable help.

Re: Aspect to vectors/polygons

LaszloKomaromi2 — Wed, 09 Nov 2016 21:12:47 GMT

The Raster Calculator tool keeps on crashing, I just can't get it started. Is there any other way to reclassify/round up values through layer properties or maybe the round up tool?

Re: Aspect to vectors/polygons

DanPatterson_Retired — Wed, 09 Nov 2016 21:36:24 GMT

why are you using the raster calculator to reclassify? There are a selection of tools in Arctoolbox to do that

like Reclassify—Help | ArcGIS for Desktop

Re: Aspect to vectors/polygons

LaszloKomaromi2 — Wed, 09 Nov 2016 22:52:30 GMT

Ok, I've got it. I used the Reclassify tool. Thanks.

Re: Aspect to vectors/polygons

DanPatterson_Retired — Wed, 09 Nov 2016 23:04:33 GMT

could you mark the thread answered then so that others will know that resolution was done