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Any help you can give an inexperienced college GIS user would be greatly appreciated.

I am using both ArcGIS ArcMap 9.3 and 10 on desktop (i.e. not online), and the only info I can find on License Type on college computers is 'ArcInfo'.

I have a set of forestry data that maps forestry type (species/age class etc) for a small country. With this data I am attempting to evaluate suitable habitat by identifying woodlands over a certain size (>200ha) with particular make up of tree species (mostly coniferous/broadleaf).

The problem I am having is that the shapefile has polygons made according to individual tree species. Is there a way to cluster the individual tree species, so I can attain one larger polygon for the entire woodland, and thereby have an area value for the woodland as a whole, instead of the individual parts (both due to seperate species, or division due to a fence, for example).

There are thousands of polygons in the dataset, so it is not feasible to get the sum individual ones, with the time I have available to me.

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    Welcome to GIS SE! What version and license level of ArcGIS for Desktop are you using? For this question it may make quite a difference. Please be sure to use the edit button to update your question with this information rather than just as a comment. – PolyGeo Aug 6 '13 at 11:25
  • Hi, thank you! I edited the post there, but I'll say it here too. I'm between 2 computers, one using ArcMap 10, and the other ArcMap 9.3. The only info I can find on licence level states that the licence type is ArcInfo... Is that what you're looking for? Thanks for your help. – user20787 Aug 7 '13 at 12:06
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You should use the Dissolve tool. By default, this will create multipart features where your stands are separated by a small gap. This is what you want for your case. You can elect to dissolve everything or by a common attribute. After dissolving you will get an accurate areas calculation. Dissolve is available in all licence types.

Aggregate Polygons will not give you the result you need because it will add additional area between the individual polygons, thus effectively increasing the area of woodland. It's a great tool but I'm not convinced it is appropriate for your use-case. For the same reason Convex Hull is also inappropriate.

  • I think you are probably correct (+1) because the asker mentioned "contiguous polygons" which I had overlooked. I'll leave my answer up for now, just in case it is still useful. – PolyGeo Aug 7 '13 at 21:52
  • Aggregate polygons is a fantastic tool nonetheless and I've used it quite a bit to generalize data. – MappaGnosis Aug 8 '13 at 7:17
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An ArcInfo or Advanced license is what you will need to use Aggregate Polygons which I think is designed for your situation. I don't think 9.3 will be as useful as 10.0 for this but 10.1/10.2 would be better.

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