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Definition: Tree canopy is defined as the layer of leaves, branches, and stems of trees that cover the ground when viewed from above.
Methods: The 2022 tree canopy layer was derived from satellite imagery (Maxar) and aerial imagery (NAIP). Images were used to extract tree canopy into GIS vector features. First, a “visual recognition engine” generated the vector features. The engine used machine learning algorithms to detect and label image pixels as tree canopy. Then using prior knowledge of feature geometries, more modeling algorithms were used to predict and transform probability maps of labeled pixels into finished vector polygons depicting tree canopy. The resulting features were reviewed and edited through manual interpretation by GIS professionals. When appropriate, NAIP 2022 aerial imagery supplemented satellite images that had cloud cover, and a manual editing process made sure tree canopy represented 2022 conditions. Finally, an independent accuracy assessment was performed by the City of Austin and the Texas A&M Forest Service for quality assurance. GIS professionals assessed agreement between the tree canopy data and its source satellite imagery. An overall accuracy of 98% was found. Only 23 errors were found out of a total 1,000 locations reviewed. These were mostly omission errors (e.g. not including canopy in this dataset when canopy is shown in the satellite or aerial image). Best efforts were made to ensure ground-truth locations contained a tree on the ground. To ensure this, location data were used from the tree inventory (City of Austin) and Urban FIA (Texas A&M Forest Service) databases.
Spatial Reference: Tree canopy data were re-projected from WGS 1984 UTM Zone 14N to NAD 1983 StatePlane Texas Central FIPS 4203 (US Feet).
Satellite imagery sourced from Maxar Technologies:
Sensor - World-View 02 (WV-02)
Collection Date - June 11, 2022
Resolution - 55 cm
Off Nadir Angle - 24.33 degrees
True Color, 3-band
Spatial Reference - WGS 1984
Sensor - Geo-Eye 01 (GE01)
Collection Date - September 28, 2022
Resolution - 49 cm
Off Nadir Angle - 44.23 degrees
True Color, 3-band
Spatial Reference - WGS 1984
Aerial imagery sourced from USDA National Agriculture Imagery Program (NAIP):
Sensor - Leica ADS100
Collection Date - June 6, 8, 10, and 11, 2022
Resolution - 60 cm
4-band CIR
Analysis: The City of Austin measures tree canopy using the calculation: acres of tree canopy divided by acres of land. The area of interest for the land acres is evaluated at the City of Austin's jurisdiction including Full Purpose, Limited Purpose, and Extraterritorial jurisdictions as of May 2023. New data show, in 2022, tree canopy covered 41% of the total land area within Austin's city limits (using city limit boundaries May 2023).
160,046.50 canopy acres (2022) / 395,037.53 land acres = 40.51% ~41%
This compares to 36% last measured in 2018, and a historical average that’s also hovered around 36%. The time period between 2018 and 2022 saw a 5 percentage point change resulting in over 19K acres of canopy gained (estimated).
Data Disclaimer: It's possible changes in percent canopy over the years is due to annexation and improved data methods (e.g. higher resolution imagery, AI, software used, etc.) in addition to actual in changes in tree canopy cover on the ground. For planning purposes only. Dataset does not account for individual trees, tree species nor any metric for tree canopy height.
Frequency: Tree canopy data updated every 4 years - 2022, 2018, 2014, 2010, and 2006.