Geographic Coverage

Coverage is measured in unique Maidenhead grid pairs (transmitter grid + receiver grid). A grid pair with at least one spot means we have a measured propagation sample for that path under some set of solar conditions. More spots per pair means better characterization of that path across varying conditions.

Grid squares are 4-character Maidenhead (e.g., EN52), giving approximately 111 km x 111 km resolution. There are 32,400 possible 4-character grid squares globally.

Grid assignments are resolved via wspr.callsign_grid — a Rosetta Stone table that maps callsigns to their most-used grid square, built from all four source datasets. 3.89M verified operators, enriched with PSK Reporter data which contributed the majority of grid assignments for callsigns not active on WSPR.