An optically independent administrative reference for validating built-surface products, and the tree-canopy bias it reveals

Reproduction package for a measurement paper on tree-canopy bias in optical built-surface products. A validation reference is built from administrative property records rather than imagery: assessor floor area divided by storey count, plus the recorded garage, summed over the parcels in a 30 m cell and taken as a share of cell area, gives a lower bound on the impervious fraction that cell holds. Because no step uses imagery, the bound cannot inherit the occlusion it is used to detect. Across 21,931 parcels in Nevada County, California, closed canopy is associated with 18 to 22 percentage points less measured NLCD impervious surface than open ground, and with a 31 point higher probability that the product reports less than the bound. The archive contains the full 24,088-record parcel census with all derived variables, the extraction and analysis code, the figure scripts and a verification harness of 522 assertions that reproduces every table, figure and quoted value from the released data. Licensing. The code is released under the MIT License. The datasets are separately dedicated to the public domain under CC0 1.0: nevada_canopy_bias_rowlevel.csv, parcel_edge_exact.csv, parcel_extras.csv, ms_footprint_validation.csv, ca_county_scan.csv and nlcd_vs_ghsl_check.csv. See the LICENSE file.