How to delineate/draw the edge of polygon automatically?

[Zihan_Lin]

I would like to delineate the edge of my extraction below, not by hand, just automatically. I want to eliminate the inside polygons and keep the outermost edge only (highlighted by blue, not accurately). Could anyone give me some hints on this part? Thank you in advance!

[DarrenWiens2]

Run Dissolve without checking any of the dissolve fields.

If you just want the outline of a few polygons, select them, then run Dissolve.

Dissolve—Data Management toolbox | ArcGIS Desktop 

[Zihan_Lin]

Thanks for the reply. Actually, the above image is what I got from running Dissolve. 

[DarrenWiens2]

Are those lines or polygons?

[Zihan_Lin]

It's a large polygon with holes inside. Sorry for lack of information.

[BlakeTerhune]

You'll probably need to manually fill the holes inside or else it's always going to consider those part of the feature when you run Dissolve.

If you wanted to do it semi-manually, you can start editing and trace the boundary you want.

Creating segments by tracing—Help | ArcGIS Desktop 

Also, you posted in the area for help using the GeoNet site. Tagging https://community.esri.com/community/gis/managing-data?sr=search&searchId=c25d959d-9dd7-4320-a287-94...‌ for better visibility.

[Zihan_Lin]

I finally manually edited the shapefile and also ran Eliminate Polygon Part tool. Thank you for the tagging suggestion. 

[DarrenWiens2]

Ah, you can try Union-ing your existing file with another feature class containing a polygon that covers your entire area, then selecting and deleting the resulting "outside" polygon, and dissolving the "inside" polygons.

[Zihan_Lin]

That's smart! I'll try. I just manually edited the shapefile and ran Eliminate Polygon Part tool. It worked. But your suggestion is so creative. 

[AbdullahAnter]

If you have Advanced license.Use Eliminate Polygon Part tool.

Eliminate Polygon Part—Help | ArcGIS Desktop 

and input maximum hole area value in Area ( optional)