This GeoPackage, WBPHS_Strata.gpkg, contains the approximate WBPHS survey design stratum boundaries for Alaska and Old Crow Flats, Yukon Territory (i.e., strata 1 through 12). Strata 1-12 were adopted in 1974 and are applied retroactively to all years of data during analyses. The strata and measurements in this GeoPackage are not accurate, because MBM-AK has been unable to locate clear, unequivocal documentation of the exact boundary delineations that were measured and adopted in 1974. Multiple versions of historical paper maps and blueprints exist on which survey designers drew stratum boundaries; however, the maps do not include documentation on what the drawn boundaries represent, i.e., whether they were draft or final versions, or which of the boundaries were adopted. In the 1990s, MBM-AK staff digitized the strata that had been drawn on a 1:1,000,000 scale topographic map for the purpose of creating various digitally-derived display products (e.g., basic report figures). Later, an attempt was made to revise the spatial layer to better match the originally designed boundaries; however, the task was not completed for all strata, due to the confusing documentation and the fact that the original boundaries did not necessarily represent optimal expansion areas anyway (and therefore, MBM-AK likely still would not use it for spatial analyses). In a few cases, the measurements of the digitized polygons are close to the published stratum-area measurements; however, in some cases they differ substantially.
Given the inaccuracy of WBPHS_Strata.gpkg, MBM-AK has used this spatial layer only for general display purposes. To produce bird abundance estimates by stratum, the stratum-area measurements that were calculated in 1974 are used.
