We have conducted an extensive study of tree canopy change in the District of Columbia from 2006 to 2011 using high-resolution imagery. This project was extremely challenging due to the numerous factors (sensor, resolution, look angle, offset, etc.) that made it very easy to falsely classify change. Despite our best efforts at an automated approach, in the end it came down to good, old-fashioned manual image interpretation. Only a human was capable of determining if the change was actual change or false change resulting from the aforementioned differences in the image datasets.
As you can see from the example below the mapping is extraordinarily detailed. We went to great pains to map change at the individual tree level and felt that this level of detail was required to account for the fine-scale change that occurs in an urban environment.
In order to solicit input from all stakeholders we are releasing this dataset for review and comment. You can download a zipped shapefile from this link. Please note that the shapefile does include metadata in XML format. The ChangeType field consists of three possible values: 1) no change, 2) loss, and 3) gain. No change indicates that the tree canopy has not changed substantially from 2006 to 2011. Loss indicates that tree canopy was removed from 2006 to 2011. Gain indicates that new tree canopy was established between 2006 and 2011.
If you have the time to evaluate this dataset we would be grateful for any feedback that you can provide.