Identify polygons that share boundary with straight lines

Anonymous User

I have a polygon dataset (10,000 + features) that was originally digitized in rectangular units (green lines) and has now been merged across the seamlines of the rectangular units using the Dissolve tool. I want to identify polygons that did not dissolve properly due to an incorrect difference in attributes (example: polygons B and C in image) or were mistakenly not digitized on the other side of the rectangular unit and appear "cut off" (polygon D). 

Essentially, I want to flag polygons that have a straight line boundaries that are coincident with (or run parallel and very close to) the boundaries of the rectangular units. Polygons that cross the unit boundaries, like polygon A, do not need to be flagged.

I have tried merging the polygon and rectangular unit layers into one dataset and running Polygon Neighbors, but that generates a table that is confusing and lists every shared polygon border (ex: information about polygon B and E's border that I am not interested in). I have also tried the "share a line segment with" relationship in Select by Location, but that has not selected the appropriate features. 

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Anonymous User

Thanks DanLee,

I modified your suggestion to get the closest-to-ideal solution: 

1. Created a copy of the blue polygons layer and ran the Snap tool (snap edges of polygons to the edges of the green boundary polygons, within 2 m) because some of these straight, parallel lines that I want to identify were slightly offset from the green polygons. 
2. Ran Polygon to Line with default settings for both the blue snapped and green polygons. 
3. Select by Location, relationship = "Share a line segment with"