Structural Intensity: Threshold Validation, Reproducibility, and Cross-City Transferability—A Technical Supplement to The Structural Urban Form of Washington, DC

<p>This technical supplement evaluates the empirical basis, reproducibility, sensitivity, external-source validation, and cross-city transferability of the Structural Intensity (SI) threshold SI ≥ 0.007987 introduced in&nbsp;<em>The Structural Urban Form of Washington, DC</em>.</p> <p>The analysis documents exact reconstruction of the Washington, DC baseline; fine-grained threshold and adjacency sensitivity tests; comparisons of Microsoft Band 1 with municipal building-footprint data in Washington, DC and Philadelphia, PA; and unchanged application of the threshold across six contrasting U.S. cities. Detailed corridor diagnostics examine how I-676 in Philadelphia and I-695 and I-395 in Washington, DC affect native-cell connectivity through surrounding built conditions rather than through a predetermined highway-barrier rule.</p> <p>The results support retaining SI ≥ 0.007987 as the fixed operational threshold and as a reproducible implementation of a broader empirical operating regime near SI 0.008. They do not establish the threshold as a theoretically unique natural constant. The supplement also distinguishes computational reproducibility from unaffiliated independent replication.</p>