This map shows 12-class land cover in the Chesapeake Bay Watershed. It was extracted from a map showing land-cover conversion in the Chesapeake Bay Watershed during the period 2013/2014-2017/2018. It was modeled with an existing 2013/2014 (Time Period 1, or T1) land-cover map containing the following classes: Water, Emergent Wetlands, Tree Canopy, Scrub\Shrub, Low Vegetation, Barren, Impervious Structures, Other Impervious, Impervious Roads, Tree Canopy Over Impervious Structures, Tree Canopy Over Other Impervious, and Tree Canopy Over Impervious Roads. Using object-based image analysis mapping techniques, the T1 map was first refined, where necessary, using all remote-sensing imagery and GIS datasets available for 2013\2014, including LiDAR, multispectral imagery, and thematic layers (e.g., roads, building footprints). The refined T1 map was then compared to imagery and GIS data corresponding to the period 2017/2018 (Time Period 1, or T2), identifying features that had changed during the analysis interval. Each change combination was assigned to a unique category that indicated both the "from" and "to" classes, enabling monitoring of specific types of change. Features that had not changed during the analysis interval were also incorporated into the change map, making it possible to reconstitute full land cover for either T1 or T2. Draft output was manually reviewed and edited to eliminate obvious errors of omission and commission, focusing on the most important types of landscape change: 1) tree-canopy loss; and 2) impervious-surfaces gain. The final map contained 79 change classes plus the original 12 classes for features that had not changed. The specific analysis periods for the watershed's 7 states\districts were: Delaware, 2013-2018; District of Columbia, 2013-2017; Maryland, 2013-2018; New York, 2013-2017; Pennsylvania, 2013-2017; Virginia, 2014-2018; and West Virginia, 2014-2018. The 12-class extract of the change-detection map was created by reassigning all change classes to their T2 status.

This map shows 12-class land cover in the Chesapeake Bay Watershed. It was extracted from a map showing land-cover conversion in the Chesapeake Bay Watershed during the period 2013/2014-2017/2018. It was modeled with an existing 2013/2014 (Time Period 1, or T1) land-cover map containing the following classes: Water, Emergent Wetlands, Tree Canopy, Scrub\Shrub, Low Vegetation, Barren, Impervious Structures, Other Impervious, Impervious Roads, Tree Canopy Over Impervious Structures, Tree Canopy Over Other Impervious, and Tree Canopy Over Impervious Roads. Using object-based image analysis mapping techniques, the T1 map was first refined, where necessary, using all remote-sensing imagery and GIS datasets available for 2013\2014, including LiDAR, multispectral imagery, and thematic layers (e.g., roads, building footprints). The refined T1 map was then compared to imagery and GIS data corresponding to the period 2017/2018 (Time Period 1, or T2), identifying features that had changed during the analysis interval. Each change combination was assigned to a unique category that indicated both the "from" and "to" classes, enabling monitoring of specific types of change. Features that had not changed during the analysis interval were also incorporated into the change map, making it possible to reconstitute full land cover for either T1 or T2. Draft output was manually reviewed and edited to eliminate obvious errors of omission and commission, focusing on the most important types of landscape change: 1) tree-canopy loss; and 2) impervious-surfaces gain. The final map contained 79 change classes plus the original 12 classes for features that had not changed. The specific analysis periods for the watershed's 7 states\districts were: Delaware, 2013-2018; District of Columbia, 2013-2017; Maryland, 2013-2018; New York, 2013-2017; Pennsylvania, 2013-2017; Virginia, 2014-2018; and West Virginia, 2014-2018. The 12-class extract of the change-detection map was created by reassigning all change classes to their T2 status.