Quantifying company-level impacts – calculation of median
footprint sizes by facility category:
We estimated a median footprint size for each asset facility category in
the S&P Physical Assets Database. For each category, asset locations
were randomly selected for measurement in GIS. If a selected asset’s
presence was visually detected and verified with high-resolution
satellite imagery, its physical footprint was traced and measured. For
all but two facility categories, areas were measured. The two remaining
categories (“transmission line” and “natural gas pipeline”) were
linear, thus their assets’ widths were measured instead. Between two and
46 assets were sampled for each facility category. The sampled assets’
measurements were used to calculate median footprint sizes (areas or
widths) for each category.
For non-linear assets, the point location or each asset was buffered to
create a circle of the appropriate area for its category.
For the linear assets, a minimum spanning tree approach was used to
connect multiple point locations by unique asset number. Then, the
calculated median width was applied to create footprints.
Table S1. Number of assets per S&P Physical Assets Database
facility category in analysis. Assets within facility categories may
fall under multiple sectors, as sectors are assigned the company level
based on a company’s principal business activity.