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I have three data sets of San Francisco, TerraSAR-X, ALOS-PALSAR, Radarsat2. I have extracted KML files using Envi Sarscape.

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In order to find the intersection of these areas, I have converted these kml's into polygon shapefiles using:

Conversion Tools ---> From KML ---> KML To Layer
Conversion Tools ---> To Shapefile ---> Feature Class To Shapefile (multiple)

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Each of those shapefiles have the following coordinate system when I used the properties from ArcCatalog

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But when I used the following toolbox to extract the intersection shapefile

Analysis Tools ---> Overlay ---> Intersect

The extracted shapefile will be as follows!!

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What's the problem?

Edit to answer radouxju
Union would give the following result

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    Are you sure that nothing is wrong with your coordinate systems / projections of the three shapefiles?
    – dru87
    Commented Feb 25, 2016 at 10:43
  • What if you project the three shapefiles to a projected coordinate system (PRCS), such as UTM? I believe Intersect Tool is using planar mathematics for the geographical coordinate system (WGS). Although that issue is patched at 10!
    – Farid Cheraghi
    Commented Feb 28, 2016 at 0:13

2 Answers 2

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Strange Union output is common with shapefiles with invalid geometries. Shapefiles are expected to follow "right hand rule" (walking the perimeter of the geometry, the feature is always on the right hand side), while KML is expected to follow "left hand rule" (except Google calls it "right hand rule", after a different rule, involving the thumb and fingers). If the polygons are wrapped incorrectly, then optimiztions in the Union code will exclude figure instead of ground.

Whenever you get unexpected output from any overlay operation (Union, Intersect, Erase,...) with a shapefile data source, you should always use Check Geometry to validate your data source. If it fails validation, then the Repair Geometry utility can be used to correct the polygon windings.

If you convert the KML to file geodatabase instead of shapefile, any improper KML winding would be either detected or corrected, since topology checks are performed when FGDB geometries are written. This is yet another reason to use file geodatabase instead of shapefile.

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That doesn't look like the sort of output I would anticipate from the Intersect tool.

If you are totally stuck, the Feature To Polygon (Data Management) tool will differentiate out the common area between your three polygons. If you then convert each polygon to a point and spatially join this back to your new polygons dataset you should be able to get a count of how many polygons each point intersects; you will be looking for those with a score of three.

A more detailed article on this workflow is available here: More adventures in overlay: counting overlapping polygons with spaghetti and meatballs.

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