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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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Merging Multipart Polygons
Now we have separate polygons for all the relevant areas. What we want are all of the polygons of a given jurisdiction as a multi-polygon feature. We do this by merging the polygons that fall under each jurisdiction.
____ 22. First select all the land polygons in the West County: Use the Select Features (by Rectangle—somewhat misnamed) tool. Hold down Shift and click each land area in the western part of the island chain. (This area includes an island that is in a lake that is on an island—look back at the image for reference to this.) You should have four polygons selected. Right-click North Islands_Polygons and pick Properties > Labels. Label all polygons with OBJECTID. Verify with the attribute table that the correct polygons are selected. Click Editor, then Start Editing. Click Editor again, then Merge. Check the information in the Merge window, click the text lines and observe the drawing. End up highlighting the polygon with the lowest number label. This will make this polygon the one with which the other three will be merged. Click OK. Clear selections with Selection > Clear Selected Features.
____ 23. In the same way, select all the lakes and merge their polygons.
____ 24. Merge the polygons of the land areas in the East County except for the volcano and its cauldron. Check your work with the Identify tool by flashing the polygons that belong to each jurisdiction. If you find an error, stop editing without saving the edits, and start again. ...

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