Research note

DGM1 topography and rigid registration.

The terrain layer derives from the verified 5 m derivative of official Geobasis NRW DGM1 data. The source array is 880 × 790 cells with observed elevation range 151.92999–290.45999 m.

The historical plan is transformed rigidly into EPSG:25832; it is not scaled or warped to eliminate OSM residuals. This preserves the historical internal geometry while allowing discrepancies with modern mapping to remain visible as uncertainty.