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I'm working with ArcGis to create a habitat mapping, so I have digitized the most part of my area with different polygons. I would like to create another one but it's really difficult because it is like a background polygon. I have to snap this polygon with all the others that I have just created. Do you know if is there a good way to do this? I wouldn't do this polygon manually.

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do the habitat polygons share boundaries with each other or are there empty spaces in between? – badkins Apr 19 '11 at 15:26
I did :) thanks I united a polygon that I created like perimeter with the other habitat polygon and I don't know how my maps seems very good and how I wanted it. – miki Apr 19 '11 at 15:34

If I understand your question correctly, you could digitize your one large habitat polygon to its own layer (not worrying about overlapping features). Then, use the Erase tool (at ArcInfo license level) to erase the large polygon with your original habitat layer. Next, you can merge the large erased habitat layer with your original layer. This will make sure your edges between the large and small polygons do not have gaps/overlaps.

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It looks like you need the symmetrical difference between them.

Create a new shapefile; digitize a big square polygon that overlaps all the other polygons (in that other layer); run symmetrical difference;

Your output will be exactly the difference of the intersection between the two layers.

To merge that result into your original shapefile/layer, you can:

Copy / Paste (don't forget to set the target correctly) inside a edit session Append (gp tool)

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If I understood you correctly, you want to unify your existing polygons to one great polygon. You can do this by using the 'Dissolve' geprocessing tool. You can find it in your toolbox under

Data Management Tools > Generalization > Dissolve

Have a look at the documentation.

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It "seems" you are asking how to create an outline of "all" the areas you've digitized. If so, just make a copy of the original shapefile (or even drop it in the map twice - doesn't matter really), and turn off the lineweight in the symbology menu (see attachment). Is this what you're aking?

enter image description here

If it's "NOT" just a graphical exercise, try the Disslove Tool

Dissolve Tool

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I think the Symmetrical Difference and Erase methods will work well if you have an ArcInfo license but with just ArcView there is a technique described at which I've used successfully to do this.

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