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I am making a model in ModelBuilder in ArcGIS Desktop 10.1.

I am using Intersect tool. I need to calculate the Shape_Area and Shape_Length of my polygons (Projected Coordinate System, EPSG: 5514, S-JTSK_Krovak_East_North).

I noticed that these values are automatically calculated and joined to attribute table when I run the Intersect tool.

Is that true for every Intersect run? Or do I need to add tools: Add field and Calculate field to be sure that my calculations of Area and Length are correct and updated after Intersection?

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The SHAPE_LENGTH and SHAPE_AREA fields are dynamic geodatabase fields. These are automatically updated when you modify a feature.

You will be unable to use the Calculate Field tool to update these fields manually.

This is fairly easy to test/verify. Here I have run the Intersect tool on two polygon layers (poly1 and poly2) to produce poly3. I have then created additional test fields in poly3 and calculated geometry in these. You will see the calculated geometry matches the automatically updated SHAPE_LENGTH and SHAPE_AREA fields.

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Note: these are not dynamic in a shapefile, only in a geodatabase. In a shapefile these are user fields that would need to be calculated if you want them up-to-date.

Also Note: The values may also be worthless if the Spatial Reference is based on a Geographic Coordinate System.

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    They may also be worthless (if the SpatialReference is based on a GCS) – Vince Feb 26 '17 at 16:59
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    I would add in, for shapefiles the shape length and shape area do not automatically update – ziggy Feb 26 '17 at 17:24

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