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Is there a way to access the classification histogram which is used when classifying data in ArcGIS desktop?

The background is I have a series of data layers for which I need to use the same classification. What I'd like to do is to be able to show the histogram for each layer in one corner of the map - possibly even with the bars coloured in the same way as the symbols.

Has anyone encountered this or does anyone have any suggestions as to how it might be done?

Classification histogram image

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I am not aware of a method to do it directly in ArcMap. You could however do it manually using the following method.

  1. In the data you want to generate the histogram for, create a field called "Class".
  2. Use the "Select by Attributes" to select the data which meets your needs (i.e) to match the classification you want to use in the Symbology / Classification Windows. From your example, the first selection would be all values that are between 0 and 1.5.
  3. Once you have made the selection, use the field calulator on the field you created in Step 1 and give it a Class ID. This can be anything, just be consistent.
  4. Repeat the select by attributes and field calculator until you have run through all possible classes and all data in your shapefile.
  5. Clear the selection in your attribute table and then select all records, Right click on the left hand side of the attribute table and select "Copy Selected Records".
  6. Open a Spreadsheet in your preferred software package (I will assume Excel) and paste the values into an empty work book. Highlight all the information and go to "Insert" and "Insert a Pivot Table".
  7. Using the Pivot Table Options on the right-hand side, select the field created in Step 1 as the "ROWS" information as well as the "VALUES". In the "VALUES" window choose to change the "Value Field Settings", make it "count".

You now have a table showing your classes and number of data points per class. If you want to replicate the Histogram exactly as it appears in ArcMap, I think you should be able to do the same thing by using the field you are trying to classify as the input field in Step 7.

You can then create a chart using the Pivot Table as the input. You can customise it as you see fit to match your map and then copy and paste it onto your Map Template when completed.

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