topic Re: Why the count does not match in Histogram and Attribute table ? in ArcGIS Spatial Analyst Questions

Why the count does not match in Histogram and Attribute table ?

MOHAMMEDHABBOUB — Thu, 22 Sep 2011 17:30:04 GMT

Hello everybody

I worked on Spatial analyst .. " Histogram"
But I have a question Why the count does not match in Histogram and Attribute table ?

see attached image

Weird, isn't it?

PLZ help

Re: Why the count does not match in Histogram and Attribute table ?

DanPatterson_Retired — Thu, 22 Sep 2011 20:03:33 GMT

grid tables give cell count which multiplied by the square of the cell width gives area...histogram, IMS...yields area...check in any event

Re: Why the count does not match in Histogram and Attribute table ?

MOHAMMEDHABBOUB — Fri, 23 Sep 2011 02:32:17 GMT

Well, It doesn't make sense.

The cell width is 25 so the area is 25*25=625
the Count in attribute table is 671722 but in Histogram is 466834

466834 + 625 =467459 not 671722

So Why?

Re: Why the count does not match in Histogram and Attribute table ?

DanPatterson_Retired — Fri, 23 Sep 2011 09:46:04 GMT

What is even stranger is the class/value shown with identify (4) doesn't match that within the raster table (6). In any event, you would multiply the cell area by the count to get area (which wouldn't help in your case anyway)

Re: Why the count does not match in Histogram and Attribute table ?

EricRice — Fri, 23 Sep 2011 19:01:20 GMT

Greetings,

Try rebuilding the raster attribute table. Some operations (tools) do not automatically update the count field. For example, if you clip a raster, the result will have count values that reflect the original counts. Maybe your table is out of sync with the data. Just a thought.

Regards,
Eric

Re: Why the count does not match in Histogram and Attribute table ?

EricRice — Fri, 23 Sep 2011 19:04:27 GMT

I just realized that is the landuse raster from the Spatial Analyst tutorial data. I'm guessing you didn't do anything to it yet that would require a rebuild of the table?

Re: Why the count does not match in Histogram and Attribute table ?

MOHAMMEDHABBOUB — Sun, 25 Sep 2011 03:03:28 GMT

That's right Eric, this is from Spatial Analysis Tutorial and I did nothing to the raster yet... so there is no point in rebuilding.

So? is it a bug? or what?

Re: Why the count does not match in Histogram and Attribute table ?

DanPatterson_Retired — Sun, 25 Sep 2011 10:21:58 GMT

did you try rebuilding to see if the original file is in error?

Re: Why the count does not match in Histogram and Attribute table ?

EricRice — Mon, 26 Sep 2011 15:41:39 GMT

Your screenshot indicates you are using an old version of the software. I can't reproduce this issue. Can you upgrade? It looks like a bug in an older product.

Regards,
Eric

Re: Why the count does not match in Histogram and Attribute table ?

MOHAMMEDHABBOUB — Tue, 27 Sep 2011 18:54:50 GMT

I will try to upgrade

Re: Why the count does not match in Histogram and Attribute table ?

RobertoRossi — Fri, 04 May 2012 16:45:06 GMT

I had the same kind of problem: when I build a histogram from the Spatial Analyst Toolbar, if I sum the frequency of the data which produce the histogram, the result doesn't match the total number of the cell of the raster.
It happens for large rasters (in my case over 3 millions cells, it is a Digital Terrain Model of a watershed).
If I use the Zonal Histogram tool (available at ArcToolBox > Spatial Analayst Tools > Zonal) the count matches perfectly. So this problem is only of the Spatial Analyst Toolbar Histogram tool.
It seems that the computation depends on some kind of sampling related to the map scale and the screen resolution, as is possible to notice from the image below:
[ATTACH=CONFIG]14102[/ATTACH]
The histogram on the left is obtained at a 1:100,000 scale, the one on center at a 1:25,000 scale, the one on the right with the Zonal Histogram tool; of the course they are all obtained from the same dataset.
This seem confirmed from what we can read from In the What's new in ArcGIS 10.1 document, at page 120: �??The interactive tools from the Spatial Analyst toolbar have been updated to operate on the data within the extent of your ArcMap window and at the screen resolution�?�.
I think anyway ESRI should address this problem in ArcGIS 10 or, at least, declare this limit on help or documentation.
I hope in the Service Pack 5.

Roberto Rossi
CIRGEO, Padua University

Re: Why the count does not match in Histogram and Attribute table ?

JuanLaguna — Mon, 07 May 2012 18:53:21 GMT

Hi all.

Just a note that the Webhelp for ArcGIS 10.0 has been updated with the improved behaviour introduced in SP4:

http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Working_with_the_Spatial_Analyst_toolbar/005900000008000000/

Regards
juan