I'm working on a project attempting to identify suitable woodland habitat for red squirrel translocation wherein conservation efforts could be focused. Below is a small section of the map showing where individual tree species polygons have been dissolved, using a 100m buffer dissolve, to appear as larger "wooded area" polygons.

For the purpose of my project, I want to identify suitable forest areas over 200ha in size, with a suitable make up of tree species. To do this I need to determine homogenous blocks as seperate from those they are not in contact with, and then determine the size and make up of these blocks. There are ~150,000 polygons in the shapefile, so manually selecting each is not a possibility.

I think some form of spatial dissolve would be most suitable, Identifying one homogenous block as "Block 1" for example, and then using Select by Attributes to create a new shapefile with only polygons ("Blocks") with an area greater than 200ha. I am, however, unsure in how to do this. (I am very limited in my knowledge of GIS, and had the help of a phd student as well as some on here in getting this far). Thank you for any help you can give.

EDIT: USing ArcGIS/ArcMap for Desktop 9.3, with ArcInfo licence type.

Individual tree species polygons dissolved (with 100m buffer dissolve) to appear as larger "wooded area" polygon

  • 1
    Which software do you currently use? You could union the buffered data (getting a multipolygon), then split the multipolygon into the polygons it consists of, then calculate the area of the polygon and select only those polygons with area > 200 ha – chriserik Aug 14 '13 at 14:30
  • Hi, Thank you for your quick response. I have edited my original post now to include my software (I am using ArcGIS/ArcMap for Desktop 9.3, with ArcInfo licence type). Is that sufficient to run the tasks you suggested? I assume I use the Union Analysis tool to get the multipolygon, but how then do I split this in to polygons again? My apologies if this is basic stuff! – user20787 Aug 14 '13 at 14:59
  • Hi! To generate single Polygons, the "Multipart to Singlepart" - function can be used (help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/…) – chriserik Aug 14 '13 at 15:24

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.