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The following picture shows the area of my problem.

I'm stuck in a problem when I started calculating area in arcmap 10.1. In the picture, I categorize my polygon into four unique labels - i.e. vegetation, sand fill, water body, built-up area. Now I want to calculate the area of these four categories. But when I opened the attribute table and try to calculate the area of each category, there are many polygons having the same gridcode. Also I tried to add another field called Name but can't. Can anyone please tell me how I can do this ?

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    It's probable you can't add a field because you're editing. How are you trying to calculate your category? There are (at least) two ways to do this, one is an advanced field calculation, the other is select the GRIDCODE using select by attributes then calculate the Name accordingly for each unique GRIDCODE value; calculate field applies to selected records but will calculate ALL records if there isn't a selection. – Michael Stimson Jun 15 '16 at 1:50
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    this is really 2 questions. In gis stackexchange it is important to view the help center how to ask good questions. the first question 1. calculate area? if you are trying to get a total area report for each category, you want to summarize on the gridcode field. question 2. you need to clarify because your picture shows you already have a field with name as the name. – Brad Nesom Jun 15 '16 at 2:25
  • I have done in the second way, you described @MichaelMiles-Stimson – Shahidul Islam Jun 15 '16 at 10:24
  • I managed to add the Name field but I can't edit this. I thought, if i, somehow, manage to edit the field, I can calculate area of each category. @BradNesom – Shahidul Islam Jun 15 '16 at 10:29
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If you already have the Name field, as your images shows, then right-click on the field header and select "Field Calculator...". In the field calculator window, enter an expression in either VB Script or Python which checks the value of GRIDCODE and returns the appropriate name for each of the four possible values.

To calculate the total area for each type of polygon, use the Summary Statistics tool (ArcToolbox > Analysis Tools > Statistics).

  • The Input Table will be your existing polygon dataset ('polygon' in your example).
  • Set your Output Table as desired.
  • The Statistics Field will be the field which contains the area. Once you have selected the field, you will also need to enter the Statistics Type of sum in the table.
  • The Case Field will be the attribute which differntiates between the polygon type (GRIDCODE in your example)

Note that when you first enter the Statistics Field, a red X will appear next the that part of the tool until you enter the statistic type into the table

enter image description here

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  • Thank you very much. It worked ! I calculated area under each GRIDCODE successfully but I can't understand how to enter an expression in VB Script or Python as I have very poor knowledge in Python. – Shahidul Islam Jun 15 '16 at 10:21
  • I think that really could be a second question. If you post it I'm sure it'll get a quick response. – Adam Jun 15 '16 at 22:16

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