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Introducing Geographic Information Systems with ArcGIS: A Workbook Approach to Learning GIS, 3rd Edition by Michael D. Kennedy

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Understanding Dissolve
If you use Dissolve to make feature class Y from feature class X, and you don’t specify any Dissolve Fields, then no lines that separated polygons in X will show up in Y. Further, the attribute table of Y will contain only the fields OBJECTID, Shape, Shape_Length, and Shape_Area.
However, suppose that you specify a Dissolve Field in the Dissolve tool window. Then, a boundary line between each pair of adjacent polygons of X is erased in Y if, and only if, the two attribute values for that field are the same for each polygon. In any event, the specified field is retained in the attribute table of Y.
For example, suppose that X has an attribute (field) titled Owner. Assume there are two polygons (one might be growing wheat and the other corn) and they are adjacent—sharing a common border. Assume now that the Dissolve tool, specifying a Dissolve Field of Owner, is run on X to produce Y. If the Owner attribute value for each is the same (say ‘Brown’), then the boundary line will not appear in Y and the attribute table will reflect a single record, with Owner ‘Brown.’ However, if ‘Brown’ owns one polygon and ‘Smith’ owns the other, then the boundary line between them will be present in Y and there will be a record in the attribute table for each polygon.
____ 1. Start ArcCatalog. Look at the geography and the table of Union_Lc_Se_So_St. Use the tool Dissolve (Data Management) to bring up the Dissolve window. For input use Union_Lc_Se_So_St. For output use ...

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