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How do you create a mask with the polygon t...   Scott Ralston Aug 10, 2002
Re: How do you create a mask with the polyg...   Jewell Brannigan Aug 14, 2002
Re: How do you create a mask with the polyg...   Scott Ralston Aug 14, 2002
Re: How do you create a mask with the polyg...   Jewell Brannigan Aug 14, 2002
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Subject How do you create a mask with the polygon tool in ArcMap? 
Author Scott Ralston 
Date Aug 10, 2002 
Message I used to use arcview and mask out a section of my raster photo with the polygon tool before classifying the pixels so it would only classify that part of the raster and not the whole thing. How do I do the same thing using the new arcmap? 
   
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Subject Re: How do you create a mask with the polygon tool in ArcMap? 
Author Jewell Brannigan 
Date Aug 14, 2002 
Message Scott,
Do you have the Spatial Analyst extension? If you do, I just took the class on it and I can tell you where to go to set the mask.

Also, I am unsure which 'polygon tool' you are talking about.

Let me know, Jewell 
  Jewell Brannigan
GIS Analyst 
   
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Subject Re: How do you create a mask with the polygon tool in ArcMap? 
Author Scott Ralston 
Date Aug 14, 2002 
Message I am analyzing areal infrared photos. I figured out the mask by creating a new polygon coverage layer, I can use the editor tool that looks like a pencil to draw polygons around parts of the image that I would like to analyze. Then under special analysis options you set the new coverage layer as the mask. I then run the categorization tool to group similar pixels into categories. Now I am trying to learn how to combine some categories and tell the area (acreage) of each category. 
   
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Subject Re: How do you create a mask with the polygon tool in ArcMap? 
Author Jewell Brannigan 
Date Aug 14, 2002 
Message Scott,
Looks like you've found where to set the mask in the Spatial Analyst extension.

On your next task, if your not deadset on getting the area from the actual raster cells themselves, I'd use the Spatial analyst 'Raster to Feature' function to get a shapefile or feature class of the polys that you need the acreage of. From the Spatial analyst menu, you want to choose 'convert'

Once you have a poly shapefile, you can download xtools 3.0 from the Arcscripts page if you don't already have it and use it to calculate acreage.
If you make a gdb featureclass, it will have a field called shape_area and this will have the areas of all the polys, you'd just need to do a little unit conversion from there.

If you need to keep it in a raster to get your acreages, take a look at this thread, maybe it'll help.
http://forums.esri.com/Thread.asp?c=93&f=982&t=70104&mc=3

Jewell
 
  Jewell Brannigan
GIS Analyst